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Pertemuan 06 el nino climate change

This document discusses how oceanographic and climatic processes impact fisheries and stock assessments. It provides background on key properties of ocean waters like temperature, salinity, and density that create structure and movement. Climate influences ocean currents, winds, and the warm pool/cold tongue convergence zone in the Pacific. The El Niño Southern Oscillation and Pacific Decadal Oscillation impact this zone and thus primary production, fish distributions, and catches. Understanding these relationships is important for fisheries management and development plans to account for natural fluctuations in fish populations.

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How do oceanographic and climatic processes impact upon fisheries (and stock assessment)
Introduction • Oceanographic and climatic factors influence the distribution and abundance of pelagic fish (through impacts on recruitment, growth and mortality), and subsequently, the distribution and activity of the fisheries that target them • Understanding the relationship between fish abundance/distribution and oceanographic and climatic factors can provide fishers, managers and scientists with an understanding of fishery variability. • This may allow management and development plans to consider fluctuations in fish biomass and availability. • With climate change, understanding these relationships may become even more important.
Basic principles • There are four key features of the ocean about which we need to be aware if we are to understand how fish populations and fisheries are influenced by the ocean: • The oceans are not uniform water masses but have a physical structure, both vertically and horizontally • This structure results from spatial differences in the properties (e.g. temperature, salinity, water pressure and other factors) of the oceans water • Oceanic waters are constantly moving and this movement can be horizontal (e.g. wind driven surface currents) or vertical (e.g. upwellings or downwellings). • The properties, structure and movement of oceanic waters are strongly influenced by climate and atmospheric processes, and conversely have a strong influence upon these…ocean and atmosphere are a coupled dynamic system
Basic principles • Subsequently….. • The structure of the water column is constantly changing depending on prevailing climatic conditions, and hence the ocean provides a heterogeneous and dynamically changing environment within which fish must survive. • We are going to now briefly look in more detail at: • Oceanic water properties, • Ocean structure, and • Movement of water within oceans. • Climatic and atmospheric influences • Each has significant implications for fish population ecology, abundance, distribution and catchability
What are the key properties and structure of oceanic waters?
Key properties of sea water - Temperature • The temperature of the oceans varies by depth and by latitude • Ocean surface temperature strongly correlates with latitude because insolation, the amount of sunlight striking Earth’s surface, is directly related to latitude, and is highest in the tropics, hence tropical waters are warmer.
Surface Mixed Layer Why are surface waters typically warmer, less salty and less dense? Deep Layer Key properties of sea water - Temperature Warmer waters are generally less dense than cooler water and therefore “sit on top” of the cooler waters (i.e. so temperature decreases with depth). In tropical and subtropical waters, there is a thermocline (depth at which rapid temperature change)
Key properties of sea water - Temperature • In the tropical Pacific Ocean, warmer waters are typically distributed westward, but can shift with climatic conditions (discussed further later). The mean, upper-ocean, thermal structure ALONG the equator in the Pacific from 140E to 100W for November 1997 The mean, upper-ocean, thermal structure ACROSS the equator in the Pacific from 8N to 8S for November 1997 Images from NOAA Pacific Marine Environmental Laboratory
Key properties of sea water - Temperature • Tropical/subtropical oceans are permanently layered with warm, less dense surface water separated from the cold, dense deep water by a thermocline. • Temperate regions have a seasonal thermocline, polar regions have none. Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
Key properties of sea water - Salinity The salinity of the oceans waters also varies by depth. More saline waters are typically denser than less saline waters and therefore tend to sink beneath less saline water (i.e. salinity increases with depth) and by latitude (relating to precipitation and evaporation) Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
 Density of sea water is a function of (related to) temperature, salinity and water pressure.  Density increases as temperature decreases and salinity increases as pressure increases.  Pressure increases regularly with depth, but temperature and salinity are more variable.  Higher salinity water can rest above lower salinity water if the higher salinity water is sufficiently warm and the lower salinity water sufficiently cold.  Pycnocline is a layer within the water column where water density changes rapidly with depth. Key properties of sea water - Density Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
 The density of oceanic waters varies by depth  Low density waters (due to heating or low salinity) lye at the surface, denser waters below.  Pycnocline is a rapid change in density with depth (similar principle to thermocline)  The pycnocline is transitional between the surface and deep layers  In the low latitudes (tropics), the pycnocline coincides with the thermocline.  Surface water in high latitudes cools, becomes dense, sinks (convects) to the sea floor and flows outward (advects) across the ocean basin. Key properties of sea water - Density Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
Why do oceanic waters move?
Ocean water movement • The waters of the ocean are constantly in motion….why is this? • There are different types of ocean water movement, including: • horizontal currents, gyres and eddies, and • vertical upwellings and downwellings. • These movements are caused by two main factors: • Wind • Gravity • The following section will discuss how these factors drive the movement of water in the ocean
Ocean movement – Currents Surface Mixed Layer Gyres Eddies Coastal Upwelling/ Downwelling Divergence based upwelling Surface currents Seamount/ Ridge Upwelling Convergence/ Gravity based downwelling Subsurface currents
Solar radiation and wind creation Low pressure (Warmer air) High pressure (Cooler air) High pressure (Cooler air) Ocean movement – Horizontal currents
 Wind-driven currents - As wind moves across the water, it drags on the water. Water moves at about 3-4% of the wind speed.  Zonal wind flow is wind moving nearly parallel to latitude as a result of Coriolis deflection. Ocean movement – Horizontal currents
Currents carry warm water poleward on the western side of basins and cooler water equatorward on the eastern side. Westerly- driven ocean currents in the trade winds, easterly-driven ocean currents in the Westerlies and deflection of the ocean currents by the continents results in a circular current, called a gyre, which occupies most of the ocean basin in each hemisphere. Source: http://www.tulane.ed u/~bianchi/Courses/ Oceanography/
Ocean movement – Vertical currents  Ocean water can also move vertically, with the two most common processes called upwelling (movement of deep water to the surface) and downwelling (movement of surface waters to the deep). Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
Ocean movement Thermohaline circulation is a density driven flow of water between ocean basins that appears largely driven by waters of the North Atlantic, where, poleward of 45 degrees (north), the density of water increases because of declining temperature and increased salinity because of evaporation or ice formation. The water sinks to a density-appropriate level and then slowly flows outward in all directions across the basin until they are blocked by a continent. Ocean basins interconnect and exchange water with each other and with the surface. Source: http://www.tulane.ed u/~bianchi/Courses/ Oceanography/
Oceanographic structure and movement - summary Differences in solar heating between areas causes differences in air pressure which results in the air moving, i.e. wind. Winds at the surface of the ocean drags on the water, causing the water to move also, i.e. creating surface currents and gyres. Some wind patterns can cause divergence of surface waters which can result in upwelling of deeper waters. Subsurface topography can also divert deep currents to the surface, as can the convergence of currents. Evaporation leading to increased salinity and water density, or cooling leading to increased density, can result in downwelling (sinking) of surface waters. The location, strength and duration of all these water movement features varies dynamically in time and space, being driven by climatic and atmospheric factors.
Oceanography and Primary Production
Oceanographic and Primary production Primary production refers to the amount of inorganic C (mainly carbon dioxide) converted to organic C (e.g. simple sugars) by microscopic algae in a process known as photosynthesis (photo – (sun) light; synthesis = to make something). Land plants also do a similar thing Primary producers represent the base of the oceanic food chain and their abundance is critical to the abundance of animals higher in the chain
Primary production Plants require sunlight, nutrients, water and carbon dioxide for photosynthesis. Phytoplankton blooms occur when light and nutrients are abundant. Other factors that influence phytoplankton growth include upwelling, turbulence, grazing intensity and turbidity. Tropics/subtropics - sunlight is abundant, but strong thermocline restricts upwelling of nutrients and results in lower productivity. High productivity can occur in areas of coastal upwelling, in the tropical waters between the gyres and at coral reefs. In temperate regions productivity is distinctly seasonal. Polar waters are nutrient-rich all year but productivity is only high in the summer when light is abundant.
Oceanography and Primary production Low productivity in the gyres, due to downwelling (opposite of process needed to bring nutrients to surface) Source: http://www.tulane.edu/~bianchi/Cours es/Oceanography/
Why is oceanography important to fisheries? “Habitat – the place where an organism (or a community of organisms) lives, including all living (biological) and nonliving (environmental) factors or conditions of the surrounding environment.” The ocean is not a homogenous uniform water mass. It is structured, it moves, and it has different properties (of temperature, salinity, density) in different areas and at different times. As a result, some areas are productive and some aren't. What does this mean for fish? The ocean also has habitats within it. An area or mass of water within the ocean which is warm, shallow, with low salinity, low nutrients and productivity, constitutes a very different set of living conditions to one which is shallow, cold, high salinity and high productivity. Deep waters constitute a very different habitat to shallow waters. Fish species have evolved different physiologies and morphologies to exploit different habitats in the ocean Tuna species are no different. e.g. Skipjack - exploit warm, shallow tropical waters. Bluefin tuna - exploit deeper, colder more temperate habitats.
Oceanography and fish populations ……the following sections are going to discuss: 1. Some of the key features of oceanographic and climate processes (and ocean habitats) of the Pacific Ocean in more detail. 2. What we currently know about the relationship between oceanographic processes and the key species targeted by pelagic fisheries in the Pacific 3. The implications of these relationships for the fisheries targeting them, and, 4. For assessments of their status and subsequent management of the fisheries.
Oceanography and climate of the Pacific
Pacific Ocean - Surface currents Three major current features are the North Pacific Subtropical Gyre, the South Pacific Subtropical Gyre, and the equatorial currents The strength and direction of the equatorial and subequatorial currents is dependant on the prevailing winds and climatic conditions 120o 140o 160o 180o 160o 140o 120o 100o 80o 0o 20o 40o 20o 40o 60o 60o SEC Subarctic Gyre Subtropical Gyre warm pool cold tongue divergence Subtropical Gyre NECC SECC NEC KUR EAC HBT convergence Major shifts occur in currents due to changes between South East Trade Wind and North West Monsoon seasons The strength and direction of the wind driven equatorial and sub- equatorial currents play a major role in the location and size of another major oceanographic feature of the Pacific, the warm- pool/cold tongue convergence zone.
Pacific Ocean – Warm Pool / Cold Tongue Warm pool Cold tongue Convergence zone In the eastern and central Pacific, wind driven movement of currents along the equator creates an upwelling that extends westward from South America…this feature is called the “cold tongue” Western equatorial Pacific - low primary production, extreme uniformity of high sea surface temperatures (SST) (up to 28° C year-round). This water mass is referred to as the “warm pool”. These two water masses meet at the “convergence zone”.
Pacific Ocean – Warm Pool / Cold Tongue Cooling in the WCPO is absent due to high rainfall causing haline stratification that prevents mixing of surface and deeper cold nutrient rich waters. However, the low nutrient, low salinity surface waters from the warm pool can move eastward on a seasonal basis under the influence of westerly wind events. The eastward movement of warm pool meets the western movement of the cold tongue, creating a convergence zone where they meet.
Pacific Ocean - El Nino Southern Oscillation Phenomena (ENSO) El Nino c) a) Warm pool Cold tongue Warm pool La Nina ENSO • Results from complex interaction between surface layers of equatorial Pacific and overlying atmosphere • Has a very significant influence on the fisheries in the Pacific Ocean • Irregular cycle of 3-7 yr • Has 3 states – El Nino, Neutral, La Nina •
Pacific Ocean - ENSO El Nino conditions – expansion of the warm pool eastwards, resulting in warmer than average waters in the central and eastern Pacific, higher rainfall in that region, a deepening of the thermocline in the east and rising of thermocline in the western region, and cooler than average waters in the western Pacific. Neutral conditions, and La Nina conditions –characterised by stronger Pacific Trade winds, the contraction of the warm pool into the equatorial western Pacific, higher rainfall in the western Pacific and lower rainfall in the eastern Pacific, a deepening of the thermocline in the west and rising of thermocline in the eastern region.
Pacific Ocean – ENSO and PDO El Nino magnitude/duration varies Measured by difference in air pressure between EPO and WPO – negative values (<-2) signify El Nino and positive values (>2) La Nina. Another climate phenomena exists for the Pacific – the Pacific Decadal Oscillation (PDO) - characterized by abrupt, but infrequent changes that are described as “climate regime shifts” PDO operates on a scale of 20-30 years, is characterised by long term shifts in average SST between the EPO and WCPO. ENSO is a pattern that can be thought of as lying on top of the large scale temperature distribution determined by the Pacific Decadal Oscillation. 1880 1890 1900 1910 1920 -4-202 SOI 1920 1930 1940 1950 1960 1970 -4-202 SOI 1970 1975 1980 1985 1990 1995 2000 2005 -4-202 SOI (*dotted line is the standard deviation calculated over the entire time series)
Pacific Ocean – Primary Production The convergence zone between the warm pool and cold tongue in equatorial Pacific is the meeting point of cool nutrient rich upwelled waters with warm surface waters from the west. Under the influence of sunlight, these conditions promote the rapid growth and reproduction of phytoplankton (i.e.; blooms). The explosion in phytoplankton population has a cascading effect through the food chain…zooplankton>>small fish>>big fish (e.g. tunas) This process takes weeks to months, during which time equatorial waters are diverging away from the equator The regions of high tuna density and catch rates can therefore be displaced somewhat from where primary productivity was initiated
Pacific Ocean – Inter-annual Primary Production El Nino (Jan 98) La Nina (Jan 99) Sea Surface Temperature Chlorophyll a During La Nina, upwelling induced primary production is enhanced in the equatorial Eastern pacific and brought by wind driven surface waters across to central and Western Pacific, which at the same time diverge north and south of the equator. During El Nino conditions, the Eastern upwelling is suppressed, but upwelling and productivity in the far western area (PNG, Phillipines, Palau) can be enhanced.
Surface currents – Seasonal and interannual variation 1st Quarter 2nd Quarter 4th Quarter 3rd Quarter 1st Quarter 2nd Quarter 4th Quarter 3rd Quarter El Nino (example year 1997) La Nina (example year 1999) Source data: www.oscar.noaa.gov ENSO – EEZ impacts There are very clear differences in seasonal surface current directions and strength that result from interannual climatic state variations, and these cause large changes in the oceanography associated with any given EEZ in the WCPO For example, current speed and direction in the FSM region during El Nino and La Nina events
January May July August October March 1997 1998 1999 ENSO – EEZ impacts There are very clear differences in seasonal sea surface temperatures that occur in Pacific EEZs, that result from interannual climatic state variations, For example, SST in the FSM region during El Nino and La Nina events
ENSO – EEZ impacts Thermal structure 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1991 1996 2001 20061991 1996 2001 2006 Thermal structure of the water column also changes dramatically with changes in climate state. For example, SST, Depth of 27C and 22C thermoclines in 5 subregions within the FSM EEZ
Summary – Oceanography of the Pacific There are three key and interacting features of the Pacific ocean-climate system that have a large influence on the distribution and abundance of the target tuna species. These are: 1. The direction and strength of the major surface currents, 2. The size and location of the warm-pool-cold tongue interaction, and 3. The overall influence/interaction of prevailing climatic conditions (in particular ENSO and PDO) on these. These are play a large role in tuna distribution, abundance and fishing success, as will be see in following sections
How are oceanographic and climatic processes relevant to fish population dynamics and stock assessment in the Pacific? WCPO tuna stock assessments take account of: 1. Growth 2. Recruitment 3. Survival 4. Movement 5. Catch rates (Abundance indices)
Oceanographic/environmental impacts on fish populations – Introduction What are the key processes that determine population biomass? 1. Growth 2. Reproduction (Recruitment) 3. Survival (or mortality)
Oceanographic/environmental impacts on fish populations – Introduction What environmental factors impact GROWTH? 1. Food availability 2. Water temperature 3. Energy expenditure (holding position in water column, so currents and turbulence etc) 4. Other
Oceanographic/environmental impacts on fish populations – Recruitment What environmental factors impact RECRUITMENT? 1. Parental condition (Nutritional status>>Food availability) 2. Food availability 3. Water temperature 4. Predation/cannibalism (of eggs, larvae) 5. Disease 6. Current speed (turbulence) and advection 7. Salinity 8. Oxygen
Oceanography impacts on fish populations - Survival • Few fish species can survive in all oceanographic conditions. Instead, fish species have evolved physiological and behavioural characteristics which allow them to exploit specific conditions. • Typically, if they move outside these “habitats” then condition and survival decline. • For example, bigeye tuna have specialised circulatory features that allow them to exploit deeper colder waters than some other species, such as skipjack tuna, are capable of.
Oceanographic/environmental impacts on fish populations – Survival What environmental factors impact SURVIVAL? 1. Predation 2. Disease 3. Food availability 4. Water temperature 5. Current speed and advection 6. Salinity 7. Oxygen Impacts vary depending on stage of development
• Numerous oceanographic factors have a significant influence on the survival of pelagic fish species, and the degree of influence often varies between different life history stages Oceanography impacts on fish populations - Survival Adults Spawning and fertilisation Eggs Hatching Maturation Juvenile stages Larvae
Vertical Movement
Climate related changes in habitat volume in the Pacific There are implications of habitat volume and variation in species vertical movements for interpretation of CPUE data and its use in stock assessments. The effect of increasing/decreasing thermocline depth on catch rates, for example, is very much species specific, and also dependant on the gear type being used.
Bigeye and yellowfin tuna movement Source: Bruno Leroy, SPC, 2007 BIGEYE TUNA YELLOWFIN TUNA FAD associated FAD associated 1. Bigeye tuna show strong diurnal vertical movement (deep during day, shallower at night) due to tracking of mesopelagic prey. Bigeye physiology enables exploitation of deeper colder lower oxygen waters. 2. Yellowfin show diurnal pattern, but mostly within mixed layer above the thermocline. YFT lack key physiological adaptations of BET that enable BET to exploit deeper waters 3. Movements differ on/off FADs for both species 4. Complicates use of CPUE data in stock assessments
Horizontal movements and oceanographic shifts in the Pacific Horizontal shifts in the warm pool correspond to changing thermocline depth and together may influence the movement of tropical tuna.
Bigeye and Yellowfin tuna movements in the Pacific in relation to Oceanographic/ Climatic factors. There are a number of theories regarding these mechanisms. Typically, a decreasing in thermocline depth is associated with higher LL CPUE for bigeye Source: Lu et al. (2001)
Oceanography impacts on fish populations - SKIPJACK Horizontal movement Displacements of tagged skipjack tuna during representative El Nino (top) and La Nina (bottom) periods. Thick arrows indicate the direction and magnitude of displacement of the skipjack CPUE gravity centre during the tag recapture periods. From (Lehodey et al, 1997) These ENSO related changes in movement pattern are not yet captured in the movement parameterisation for MFCL assessments El Nino period La Nina period
2002 (-) 2000 (+) DFADs: allow fishing in east in non-El Niño periods AFADs: allow fishing in west in all years Changes in the depth of the thermocline also impacts on catchability of fish by longline fisheries Skipjack tuna and climate/oceanographic processes– Basin wide and EEZ impacts
Bigeye and yellowfin tuna Bigeye tuna Yellowfin tuna
Climate Change Uncertainty remains on the change in the productivity of the western equatorial Pacific. The impact of climate change on tuna recruitment and spawning migration is also poorly known. Current thinking is that climate change may lead to a shift in the spatial tuna distribution, as well as possible changes in productivity, total abundance and total catch in different regions.

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Pertemuan 06 el nino climate change

  • 1.
    How do oceanographicand climatic processes impact upon fisheries (and stock assessment)
  • 2.
    Introduction • Oceanographic andclimatic factors influence the distribution and abundance of pelagic fish (through impacts on recruitment, growth and mortality), and subsequently, the distribution and activity of the fisheries that target them • Understanding the relationship between fish abundance/distribution and oceanographic and climatic factors can provide fishers, managers and scientists with an understanding of fishery variability. • This may allow management and development plans to consider fluctuations in fish biomass and availability. • With climate change, understanding these relationships may become even more important.
  • 3.
    Basic principles • Thereare four key features of the ocean about which we need to be aware if we are to understand how fish populations and fisheries are influenced by the ocean: • The oceans are not uniform water masses but have a physical structure, both vertically and horizontally • This structure results from spatial differences in the properties (e.g. temperature, salinity, water pressure and other factors) of the oceans water • Oceanic waters are constantly moving and this movement can be horizontal (e.g. wind driven surface currents) or vertical (e.g. upwellings or downwellings). • The properties, structure and movement of oceanic waters are strongly influenced by climate and atmospheric processes, and conversely have a strong influence upon these…ocean and atmosphere are a coupled dynamic system
  • 4.
    Basic principles • Subsequently….. •The structure of the water column is constantly changing depending on prevailing climatic conditions, and hence the ocean provides a heterogeneous and dynamically changing environment within which fish must survive. • We are going to now briefly look in more detail at: • Oceanic water properties, • Ocean structure, and • Movement of water within oceans. • Climatic and atmospheric influences • Each has significant implications for fish population ecology, abundance, distribution and catchability
  • 5.
    What are thekey properties and structure of oceanic waters?
  • 6.
    Key properties ofsea water - Temperature • The temperature of the oceans varies by depth and by latitude • Ocean surface temperature strongly correlates with latitude because insolation, the amount of sunlight striking Earth’s surface, is directly related to latitude, and is highest in the tropics, hence tropical waters are warmer.
  • 7.
    Surface Mixed Layer Whyare surface waters typically warmer, less salty and less dense? Deep Layer Key properties of sea water - Temperature Warmer waters are generally less dense than cooler water and therefore “sit on top” of the cooler waters (i.e. so temperature decreases with depth). In tropical and subtropical waters, there is a thermocline (depth at which rapid temperature change)
  • 8.
    Key properties ofsea water - Temperature • In the tropical Pacific Ocean, warmer waters are typically distributed westward, but can shift with climatic conditions (discussed further later). The mean, upper-ocean, thermal structure ALONG the equator in the Pacific from 140E to 100W for November 1997 The mean, upper-ocean, thermal structure ACROSS the equator in the Pacific from 8N to 8S for November 1997 Images from NOAA Pacific Marine Environmental Laboratory
  • 9.
    Key properties ofsea water - Temperature • Tropical/subtropical oceans are permanently layered with warm, less dense surface water separated from the cold, dense deep water by a thermocline. • Temperate regions have a seasonal thermocline, polar regions have none. Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
  • 10.
    Key properties ofsea water - Salinity The salinity of the oceans waters also varies by depth. More saline waters are typically denser than less saline waters and therefore tend to sink beneath less saline water (i.e. salinity increases with depth) and by latitude (relating to precipitation and evaporation) Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
  • 11.
     Density ofsea water is a function of (related to) temperature, salinity and water pressure.  Density increases as temperature decreases and salinity increases as pressure increases.  Pressure increases regularly with depth, but temperature and salinity are more variable.  Higher salinity water can rest above lower salinity water if the higher salinity water is sufficiently warm and the lower salinity water sufficiently cold.  Pycnocline is a layer within the water column where water density changes rapidly with depth. Key properties of sea water - Density Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
  • 12.
     The densityof oceanic waters varies by depth  Low density waters (due to heating or low salinity) lye at the surface, denser waters below.  Pycnocline is a rapid change in density with depth (similar principle to thermocline)  The pycnocline is transitional between the surface and deep layers  In the low latitudes (tropics), the pycnocline coincides with the thermocline.  Surface water in high latitudes cools, becomes dense, sinks (convects) to the sea floor and flows outward (advects) across the ocean basin. Key properties of sea water - Density Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
  • 13.
    Why do oceanicwaters move?
  • 14.
    Ocean water movement •The waters of the ocean are constantly in motion….why is this? • There are different types of ocean water movement, including: • horizontal currents, gyres and eddies, and • vertical upwellings and downwellings. • These movements are caused by two main factors: • Wind • Gravity • The following section will discuss how these factors drive the movement of water in the ocean
  • 15.
    Ocean movement –Currents Surface Mixed Layer Gyres Eddies Coastal Upwelling/ Downwelling Divergence based upwelling Surface currents Seamount/ Ridge Upwelling Convergence/ Gravity based downwelling Subsurface currents
  • 16.
    Solar radiation andwind creation Low pressure (Warmer air) High pressure (Cooler air) High pressure (Cooler air) Ocean movement – Horizontal currents
  • 17.
     Wind-driven currents- As wind moves across the water, it drags on the water. Water moves at about 3-4% of the wind speed.  Zonal wind flow is wind moving nearly parallel to latitude as a result of Coriolis deflection. Ocean movement – Horizontal currents
  • 18.
    Currents carry warmwater poleward on the western side of basins and cooler water equatorward on the eastern side. Westerly- driven ocean currents in the trade winds, easterly-driven ocean currents in the Westerlies and deflection of the ocean currents by the continents results in a circular current, called a gyre, which occupies most of the ocean basin in each hemisphere. Source: http://www.tulane.ed u/~bianchi/Courses/ Oceanography/
  • 19.
    Ocean movement –Vertical currents  Ocean water can also move vertically, with the two most common processes called upwelling (movement of deep water to the surface) and downwelling (movement of surface waters to the deep). Source: http://www.tulane.edu/~bianchi/Courses/Oceanography/
  • 20.
    Ocean movement Thermohaline circulationis a density driven flow of water between ocean basins that appears largely driven by waters of the North Atlantic, where, poleward of 45 degrees (north), the density of water increases because of declining temperature and increased salinity because of evaporation or ice formation. The water sinks to a density-appropriate level and then slowly flows outward in all directions across the basin until they are blocked by a continent. Ocean basins interconnect and exchange water with each other and with the surface. Source: http://www.tulane.ed u/~bianchi/Courses/ Oceanography/
  • 21.
    Oceanographic structure andmovement - summary Differences in solar heating between areas causes differences in air pressure which results in the air moving, i.e. wind. Winds at the surface of the ocean drags on the water, causing the water to move also, i.e. creating surface currents and gyres. Some wind patterns can cause divergence of surface waters which can result in upwelling of deeper waters. Subsurface topography can also divert deep currents to the surface, as can the convergence of currents. Evaporation leading to increased salinity and water density, or cooling leading to increased density, can result in downwelling (sinking) of surface waters. The location, strength and duration of all these water movement features varies dynamically in time and space, being driven by climatic and atmospheric factors.
  • 22.
  • 23.
    Oceanographic and Primaryproduction Primary production refers to the amount of inorganic C (mainly carbon dioxide) converted to organic C (e.g. simple sugars) by microscopic algae in a process known as photosynthesis (photo – (sun) light; synthesis = to make something). Land plants also do a similar thing Primary producers represent the base of the oceanic food chain and their abundance is critical to the abundance of animals higher in the chain
  • 24.
    Primary production Plants requiresunlight, nutrients, water and carbon dioxide for photosynthesis. Phytoplankton blooms occur when light and nutrients are abundant. Other factors that influence phytoplankton growth include upwelling, turbulence, grazing intensity and turbidity. Tropics/subtropics - sunlight is abundant, but strong thermocline restricts upwelling of nutrients and results in lower productivity. High productivity can occur in areas of coastal upwelling, in the tropical waters between the gyres and at coral reefs. In temperate regions productivity is distinctly seasonal. Polar waters are nutrient-rich all year but productivity is only high in the summer when light is abundant.
  • 25.
    Oceanography and Primary production Lowproductivity in the gyres, due to downwelling (opposite of process needed to bring nutrients to surface) Source: http://www.tulane.edu/~bianchi/Cours es/Oceanography/
  • 26.
    Why is oceanographyimportant to fisheries? “Habitat – the place where an organism (or a community of organisms) lives, including all living (biological) and nonliving (environmental) factors or conditions of the surrounding environment.” The ocean is not a homogenous uniform water mass. It is structured, it moves, and it has different properties (of temperature, salinity, density) in different areas and at different times. As a result, some areas are productive and some aren't. What does this mean for fish? The ocean also has habitats within it. An area or mass of water within the ocean which is warm, shallow, with low salinity, low nutrients and productivity, constitutes a very different set of living conditions to one which is shallow, cold, high salinity and high productivity. Deep waters constitute a very different habitat to shallow waters. Fish species have evolved different physiologies and morphologies to exploit different habitats in the ocean Tuna species are no different. e.g. Skipjack - exploit warm, shallow tropical waters. Bluefin tuna - exploit deeper, colder more temperate habitats.
  • 27.
    Oceanography and fishpopulations ……the following sections are going to discuss: 1. Some of the key features of oceanographic and climate processes (and ocean habitats) of the Pacific Ocean in more detail. 2. What we currently know about the relationship between oceanographic processes and the key species targeted by pelagic fisheries in the Pacific 3. The implications of these relationships for the fisheries targeting them, and, 4. For assessments of their status and subsequent management of the fisheries.
  • 28.
  • 29.
    Pacific Ocean -Surface currents Three major current features are the North Pacific Subtropical Gyre, the South Pacific Subtropical Gyre, and the equatorial currents The strength and direction of the equatorial and subequatorial currents is dependant on the prevailing winds and climatic conditions 120o 140o 160o 180o 160o 140o 120o 100o 80o 0o 20o 40o 20o 40o 60o 60o SEC Subarctic Gyre Subtropical Gyre warm pool cold tongue divergence Subtropical Gyre NECC SECC NEC KUR EAC HBT convergence Major shifts occur in currents due to changes between South East Trade Wind and North West Monsoon seasons The strength and direction of the wind driven equatorial and sub- equatorial currents play a major role in the location and size of another major oceanographic feature of the Pacific, the warm- pool/cold tongue convergence zone.
  • 30.
    Pacific Ocean –Warm Pool / Cold Tongue Warm pool Cold tongue Convergence zone In the eastern and central Pacific, wind driven movement of currents along the equator creates an upwelling that extends westward from South America…this feature is called the “cold tongue” Western equatorial Pacific - low primary production, extreme uniformity of high sea surface temperatures (SST) (up to 28° C year-round). This water mass is referred to as the “warm pool”. These two water masses meet at the “convergence zone”.
  • 31.
    Pacific Ocean –Warm Pool / Cold Tongue Cooling in the WCPO is absent due to high rainfall causing haline stratification that prevents mixing of surface and deeper cold nutrient rich waters. However, the low nutrient, low salinity surface waters from the warm pool can move eastward on a seasonal basis under the influence of westerly wind events. The eastward movement of warm pool meets the western movement of the cold tongue, creating a convergence zone where they meet.
  • 32.
    Pacific Ocean -El Nino Southern Oscillation Phenomena (ENSO) El Nino c) a) Warm pool Cold tongue Warm pool La Nina ENSO • Results from complex interaction between surface layers of equatorial Pacific and overlying atmosphere • Has a very significant influence on the fisheries in the Pacific Ocean • Irregular cycle of 3-7 yr • Has 3 states – El Nino, Neutral, La Nina •
  • 33.
    Pacific Ocean -ENSO El Nino conditions – expansion of the warm pool eastwards, resulting in warmer than average waters in the central and eastern Pacific, higher rainfall in that region, a deepening of the thermocline in the east and rising of thermocline in the western region, and cooler than average waters in the western Pacific. Neutral conditions, and La Nina conditions –characterised by stronger Pacific Trade winds, the contraction of the warm pool into the equatorial western Pacific, higher rainfall in the western Pacific and lower rainfall in the eastern Pacific, a deepening of the thermocline in the west and rising of thermocline in the eastern region.
  • 34.
    Pacific Ocean –ENSO and PDO El Nino magnitude/duration varies Measured by difference in air pressure between EPO and WPO – negative values (<-2) signify El Nino and positive values (>2) La Nina. Another climate phenomena exists for the Pacific – the Pacific Decadal Oscillation (PDO) - characterized by abrupt, but infrequent changes that are described as “climate regime shifts” PDO operates on a scale of 20-30 years, is characterised by long term shifts in average SST between the EPO and WCPO. ENSO is a pattern that can be thought of as lying on top of the large scale temperature distribution determined by the Pacific Decadal Oscillation. 1880 1890 1900 1910 1920 -4-202 SOI 1920 1930 1940 1950 1960 1970 -4-202 SOI 1970 1975 1980 1985 1990 1995 2000 2005 -4-202 SOI (*dotted line is the standard deviation calculated over the entire time series)
  • 35.
    Pacific Ocean –Primary Production The convergence zone between the warm pool and cold tongue in equatorial Pacific is the meeting point of cool nutrient rich upwelled waters with warm surface waters from the west. Under the influence of sunlight, these conditions promote the rapid growth and reproduction of phytoplankton (i.e.; blooms). The explosion in phytoplankton population has a cascading effect through the food chain…zooplankton>>small fish>>big fish (e.g. tunas) This process takes weeks to months, during which time equatorial waters are diverging away from the equator The regions of high tuna density and catch rates can therefore be displaced somewhat from where primary productivity was initiated
  • 36.
    Pacific Ocean –Inter-annual Primary Production El Nino (Jan 98) La Nina (Jan 99) Sea Surface Temperature Chlorophyll a During La Nina, upwelling induced primary production is enhanced in the equatorial Eastern pacific and brought by wind driven surface waters across to central and Western Pacific, which at the same time diverge north and south of the equator. During El Nino conditions, the Eastern upwelling is suppressed, but upwelling and productivity in the far western area (PNG, Phillipines, Palau) can be enhanced.
  • 37.
    Surface currents – Seasonaland interannual variation 1st Quarter 2nd Quarter 4th Quarter 3rd Quarter 1st Quarter 2nd Quarter 4th Quarter 3rd Quarter El Nino (example year 1997) La Nina (example year 1999) Source data: www.oscar.noaa.gov ENSO – EEZ impacts There are very clear differences in seasonal surface current directions and strength that result from interannual climatic state variations, and these cause large changes in the oceanography associated with any given EEZ in the WCPO For example, current speed and direction in the FSM region during El Nino and La Nina events
  • 38.
    January May July August October March 1997 1998 1999 ENSO– EEZ impacts There are very clear differences in seasonal sea surface temperatures that occur in Pacific EEZs, that result from interannual climatic state variations, For example, SST in the FSM region during El Nino and La Nina events
  • 39.
    ENSO – EEZ impacts Thermal structure 19982000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2728293031 Seasurfacetemp. 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 2060100140 Depth(m)of27Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1998 2000 2002 2004 2006 60100140180 Depth(m)of22Cthermocline 1991 1996 2001 20061991 1996 2001 2006 Thermal structure of the water column also changes dramatically with changes in climate state. For example, SST, Depth of 27C and 22C thermoclines in 5 subregions within the FSM EEZ
  • 40.
    Summary – Oceanographyof the Pacific There are three key and interacting features of the Pacific ocean-climate system that have a large influence on the distribution and abundance of the target tuna species. These are: 1. The direction and strength of the major surface currents, 2. The size and location of the warm-pool-cold tongue interaction, and 3. The overall influence/interaction of prevailing climatic conditions (in particular ENSO and PDO) on these. These are play a large role in tuna distribution, abundance and fishing success, as will be see in following sections
  • 41.
    How are oceanographicand climatic processes relevant to fish population dynamics and stock assessment in the Pacific? WCPO tuna stock assessments take account of: 1. Growth 2. Recruitment 3. Survival 4. Movement 5. Catch rates (Abundance indices)
  • 42.
    Oceanographic/environmental impacts on fishpopulations – Introduction What are the key processes that determine population biomass? 1. Growth 2. Reproduction (Recruitment) 3. Survival (or mortality)
  • 43.
    Oceanographic/environmental impacts on fishpopulations – Introduction What environmental factors impact GROWTH? 1. Food availability 2. Water temperature 3. Energy expenditure (holding position in water column, so currents and turbulence etc) 4. Other
  • 44.
    Oceanographic/environmental impacts on fishpopulations – Recruitment What environmental factors impact RECRUITMENT? 1. Parental condition (Nutritional status>>Food availability) 2. Food availability 3. Water temperature 4. Predation/cannibalism (of eggs, larvae) 5. Disease 6. Current speed (turbulence) and advection 7. Salinity 8. Oxygen
  • 45.
    Oceanography impacts onfish populations - Survival • Few fish species can survive in all oceanographic conditions. Instead, fish species have evolved physiological and behavioural characteristics which allow them to exploit specific conditions. • Typically, if they move outside these “habitats” then condition and survival decline. • For example, bigeye tuna have specialised circulatory features that allow them to exploit deeper colder waters than some other species, such as skipjack tuna, are capable of.
  • 46.
    Oceanographic/environmental impacts on fishpopulations – Survival What environmental factors impact SURVIVAL? 1. Predation 2. Disease 3. Food availability 4. Water temperature 5. Current speed and advection 6. Salinity 7. Oxygen Impacts vary depending on stage of development
  • 47.
    • Numerous oceanographicfactors have a significant influence on the survival of pelagic fish species, and the degree of influence often varies between different life history stages Oceanography impacts on fish populations - Survival Adults Spawning and fertilisation Eggs Hatching Maturation Juvenile stages Larvae
  • 48.
  • 49.
    Climate related changesin habitat volume in the Pacific There are implications of habitat volume and variation in species vertical movements for interpretation of CPUE data and its use in stock assessments. The effect of increasing/decreasing thermocline depth on catch rates, for example, is very much species specific, and also dependant on the gear type being used.
  • 50.
    Bigeye and yellowfintuna movement Source: Bruno Leroy, SPC, 2007 BIGEYE TUNA YELLOWFIN TUNA FAD associated FAD associated 1. Bigeye tuna show strong diurnal vertical movement (deep during day, shallower at night) due to tracking of mesopelagic prey. Bigeye physiology enables exploitation of deeper colder lower oxygen waters. 2. Yellowfin show diurnal pattern, but mostly within mixed layer above the thermocline. YFT lack key physiological adaptations of BET that enable BET to exploit deeper waters 3. Movements differ on/off FADs for both species 4. Complicates use of CPUE data in stock assessments
  • 51.
    Horizontal movements andoceanographic shifts in the Pacific Horizontal shifts in the warm pool correspond to changing thermocline depth and together may influence the movement of tropical tuna.
  • 52.
    Bigeye and Yellowfintuna movements in the Pacific in relation to Oceanographic/ Climatic factors. There are a number of theories regarding these mechanisms. Typically, a decreasing in thermocline depth is associated with higher LL CPUE for bigeye Source: Lu et al. (2001)
  • 53.
    Oceanography impacts onfish populations - SKIPJACK Horizontal movement Displacements of tagged skipjack tuna during representative El Nino (top) and La Nina (bottom) periods. Thick arrows indicate the direction and magnitude of displacement of the skipjack CPUE gravity centre during the tag recapture periods. From (Lehodey et al, 1997) These ENSO related changes in movement pattern are not yet captured in the movement parameterisation for MFCL assessments El Nino period La Nina period
  • 54.
    2002 (-) 2000 (+) DFADs:allow fishing in east in non-El Niño periods AFADs: allow fishing in west in all years Changes in the depth of the thermocline also impacts on catchability of fish by longline fisheries Skipjack tuna and climate/oceanographic processes– Basin wide and EEZ impacts
  • 55.
    Bigeye and yellowfintuna Bigeye tuna Yellowfin tuna
  • 56.
    Climate Change Uncertainty remainson the change in the productivity of the western equatorial Pacific. The impact of climate change on tuna recruitment and spawning migration is also poorly known. Current thinking is that climate change may lead to a shift in the spatial tuna distribution, as well as possible changes in productivity, total abundance and total catch in different regions.

Editor's Notes