Emily A. Fergusson

Lack of trophic competition among wild and hatchery juvenile chum salmon during early marine residence in Taku Inlet, Southeast Alaska

Early marine trophic interactions of wild and hatchery chum salmon (Oncorhynchus keta) were examined as a potential cause for the decline in harvests of adult wild chum salmon in Taku Inlet, Southeast Alaska. In 2004 and 2005, outmigrating juvenile chum salmon were sampled in nearshore habitats of the inlet (spring) and in epipelagic habitat at Icy Strait (summer) as they approached the Gulf of Alaska. Fish were frozen for energy density determination or preserved for diet analyses, and hatchery stocks were identified from the presence of thermal marks on otoliths. We compared feeding intensity, diets, energy density, and size relationships of wild and hatchery stocks (n = 3123) across locations and weeks. Only hatchery fish feeding intensity was negatively correlated with fish abundance. In both years, hatchery chum salmon were initially larger and had greater energy density than wild fish, but lost condition in early weeks after release as they adapted to feeding on wild prey assemblages. Diets differed between the stocks at all inlet locations, but did not differ for hatchery salmon between littoral and neritic habitats in the outer inlet, where the stocks overlapped most. Both diets and energy density converged by late June. Therefore, if density-dependent interactions affect wild chum salmon, these effects must be very rapid because survivors in Icy Strait showed few differences. Our study also demonstrates that hatchery release strategies used near Taku Inlet successfully promote early spatial segregation and prey partitioning, which reduce the probability of competition between wild and hatchery chum salmon stocks.

Chinook Salmon First-Year Production Indicators from Ocean Monitoring in Southeast Alaska

Understanding migration and abundance of Chinook salmon stocks during critical early marine periods is important because declining returns in some regions of Alaska have eff ectuated commercial fi shery disaster declarations since 2012. Annual ocean catch data of juvenile and immature Chinook salmon pre-recruits were examined from research surface trawling in Icy Strait, Southeast Alaska (SEAK), from 1997 to 2014 to examine how ocean survival depends on critical early periods. In total, 1,108 Chinook salmon were sampled in 1,037 trawl hauls from May to September. Data on the release location and timing for 50 fi sh recovered with coded-wire tags (CWTs) indicated most to be of SEAK origin (48), and either immature (ocean age-1) or juvenile (ocean age-0). Based on monthly CWT Chinook salmon recoveries and catch, juvenile fi sh occurred in increasing abundance from June to September, whereas immature fi sh occurred in decreasing abundance from May to September. There was strong coherence in the ocean survival rates of wild and hatchery SEAK stocks of Chinook salmon, and average regional survival was signifi cantly (p < 0.05) correlated to the abundance of ocean age-1 fi sh, but not ocean age-0 fi sh. This study indicates SEAK Chinook salmon stocks have initial localized marine distributions as juveniles, and they are present as immature fi sh in the ensuing spring and summer. Research catch rates of pre-recruits have the potential to be useful as a leading ecosystem indicator stock assessment tool for managers.

Using Salmon Survey and Commercial Fishery Data to Index Nearshore Rearing Conditions and Recruitment of Alaskan Sablefish

Abstract We examined physical and biological indices from Pacific salmon Oncorhynchus spp. surveys and commercial fisheries to index nearshore rearing habitats used by age-0 and age-1 Sablefish Anoplopoma fimbria in the eastern Gulf of Alaska and as indicators for their recruitment to age2 during the period 2001–2013. The best-fitting general linear model used to estimate age-2 Sablefish recruitment included chlorophyll-a concentration during late August and an index of juvenile Pink Salmon O. gorbuscha abundance during the age-0 stage of Sablefish. The model and biophysical indices from 2012 and 2013 produced a forecast of 23 million age-2 Sablefish for 2014 and a forecast of 8 million Sablefish for 2015. This study highlights the opportunity to use proxies for direct ambient physical and biological observations of rearing habitats in estimating groundfish recruitment to older ages.