Mortality of incidentally caught and released sablefish (Anoplopoma fimbria) on longline gear in Alaska
Mortality of incidentally caught and released sablefish (Anoplopoma fimbria) on longline gear in Alaska Megan Stachura1, Chris Lunsford2, Cara Rodgveller 2, and Jon Heifetz2 1 University of Miami, Rosenstiel School of Marine and Atmospheric Science; 2 National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service (NMFS) Results Map of tagging area Hooked sablefish on longline gear on-bottom What affected recovery rates? Four parameters significantly affected whether or not a fish was recovered: 1. Year of capture 2. Depth of capture 3. Severity of hooking injury 4. Severity of amphipod predation Recovery by year of capture Recovery by depth of capture IntroductionBackground: The sablefish, Anoplopoma fimbria, is a commercially important fish as the secondhighest valued fish per pound in Alaska.Problem: In Alaska, sablefish are primarily harvested using a longline fished on-bottom at depthsfrom 200-800 m and are often caught incidentally in other hook-and-line fisheries and released.Managers currently do not account for discard mortality in mortality estimates and there is noclear indicator that can be used to estimate the mortality of released sablefish. Previous researchin other fish species have found incidental hooking mortality can be high depending on the Recovery by severity of hooking injury Recovery by amphipod predation severitylocation or severity of the hooking injury.Objective: Tag and release hook caught sablefish and estimate discard mortality based on relativerecovery rates of tagged fish for different categories of injuries. Methods 1989 and 1990 using commercialField Sampling: 10,508 sablefish were caught and tagged inlongline fishing gear in deep waters of southeast Alaska.Injuries were classified and recorded for four categories: 1. Hooking injury location 2. Hooking injury severity 3. Amphipod predation severity 4. Injury sustained from the line or roller gear Discussion Year was found to be significant. The year effect may be due to the geographic differenceOf the fish tagged, 1, 207 were later recovered in research surveys and the commercial fishery. between years, seasonal differences in tagging, or differences in unmeasured environmentalData Analysis: A logistic regression model was fit to the data with a binary response indicating if factors.the fish was recovered or not recovered. Seven explanatory variables were used: Fish caught at deeper depths had a greater recovery rate. This may be because fish caught at 1. Year of capture deep depths have less vigor than fish caught at shallower depths and fight less when being brought 2. Fish length at capture on-board so they may not become as stressed or injured. However, this finding contradicts 3. Capture depth previous research and should be investigated further. 4. Location of hooking injury The severity of the hooking injury was also found to be an important predictor of recovery, 5. Severity of hooking injury with lower recovery resulting from more severe injuries. This important finding has been 6. Severity of amphipod predation previously been observed in other species, but was not previously investigated in sablefish. 7. Injury sustained from fishing gear Amphipod predation was another factor that negatively influenced the recovery rate ofThe full model was reduced through forward-step selection by choosing the model with the sablefish. The soak time and location where gear is set may be good indicators of amphipodminimum Akaike Information Criteria (AIC) value. predation but further research regarding the influences of these factors is necessary. Amphipod Predation Injuries Important things learned from this study: • The severity of a hook injury matters more than the location • Any amphipod predation is bad for sablefish • Mortality of incidentally caught sablefish likely occurs What this study tells us: • Reducing hooking injuries probably helps reduce mortality • Managers should consider accounting for incidental hooking mortality in the sablefish stock Hooking Injuries assessment Acknowledgements This research was funded by the National Oceanic and Atmospheric Administration (NOAA) Ernest F. Hollings Undergraduate Scholarship Program. Special thanks to Cindy Tribuzio and Nancy Maloney at NOAA NMFS and Daniel DiResta, Jerald Ault, Jill Richardson, and Gary Thomas at the University of Miami for their help with this project.