Effects of inbreeding and family origin on size of chinook salmon (Oncorhynchus tshawytscha) fry

Thesis (M.S.) University of Alaska Fairbanks, 2004We cultured separate lines of chinook salmon fry of Chickamin River, Southeast Alaska, ancestry in seven common garden enclosures. A parentage analysis based on variation of microsatellite alleles showed that within these lines seven brother sister matings created 35 inbred fish from 7 families (F = 0.25) and 37 outbred fish resulted from 10 matings between segregated lines. Outbred and inbred fish did not differ in length (P = 0.42), weight (P = 0.86), or condition factor (P = 0.16). There was significant variation among families for length (P = 0.01) and weight (P <0.01), but not for condition factor (P = 0.48). Because variation among families can be large, it can potentially confound the effects for which a study was designed. To avoid drawing improper conclusions, studies should estimate the amount of variation that can be attributed to family origin, or be certain that many families are sampled

Effects of maternal age and size on embryonic energy reserves, developmental timing, and fecundity in quillback rockfish (Sebastes maliger)

Maternal effects on the quality of progeny can have direct impacts on population productivity. Rockfish are viviparous and the oil globule size of larvae at parturition has been shown to have direct effects on time until starvation and growth rate. We sampled embryos and preparturition larvae opportunistically from 89 gravid quillback rockfish (Sebastes maliger) in Southeast Alaska. Because the developmental stage and sampling period were correlated with oil globule size, they were treated as covariates in an analysis of maternal age, length, and weight effects on oil globule size. Maternal factors were related to developmental timing for almost all sampling periods, indicating that older, longer, and heavier females develop embryos earlier than younger, shorter, or lighter ones. Oil globule diameter and maternal length and weight were statistically linked, but the relationships may not be biologically significant. Weight-specific fecundity did not increase with maternal size or age, suggesting that reproductive output does not increase more quickly as fish age and grow. Age or size truncation of a rockfish population, in which timing of parturition is related to age and size, could result in a shorter parturition season. This shortening of the parturition season could make the population vulnerable to fluctuating environmental conditions

Evidence of hook competition in longline surveys

Catch rates from surveys are used as indices of abundance for many fish species. Relative abundance estimates from surveys with longline gear do not usually account for possible effects of gear saturation, which potentially creates competition among fish for baited hooks and misrepresentations of abundance trends. We examined correlations between catch rates of sablefish (Anoplopoma fimbria) and giant grenadier (Albatrossia pectoralis) and between sablefish and shortraker (Sebastes borealis) and rougheye rockfish (Sebastes aleutianus) from 25 years of longline surveys in Alaska waters for evidence of competition for hooks. Sablefish catch rates were negatively correlated with giant grenadier catch rates in all management areas in Alaskan waters, and sablefish and rockfish were negatively correlated in five of the six areas, indicating that there is likely competition for hooks during longline surveys. Comparative analyses were done for trawl survey catch rates, and no negative correlations were observed, indicating that the negative correlations on the longline surveys are not due to differing habitat preferences or direct competition. Available adjustments for gear saturation may be biased if the probability of capture does not decrease linearly with baited hooks. A better understanding of each fish species’ catch probabilities on longline gear are needed before adjustments for hook competition can be made

Estimation of discard mortality of sablefish (Anoplopoma fimbria) in Alaska longline fisheries

Sablefish (Anoplopoma fimbria) are often caught incidentally in longline fisheries and discarded, but the extent of mortality after release is unknown, which creates uncertainty for estimates of total mortality. We analyzed data from 10,427 fish that were tagged in research surveys and recovered in surveys and commercial fisheries up to 19 years later and found a decrease in recapture rates for fish originally captured at shallower depths (210–319 m) during the study, sustaining severe hooking injuries, and sustaining amphipod predation injuries. The overall estimated discard mortality rate was 11.71%. This estimate is based on an assumed survival rate of 96.5% for fish with minor hooking injuries and the observed recapture rates for sablefish at each level of severity of hook injury. This estimate may be lower than what actually occurs in commercial fisheries because fish are likely not handled as carefully as those in our study. Comparing our results with data on the relative occurrence of the severity of hooking injuries in longline fisheries may lead to more accurate accounting of total mortality attributable to fishing and to improved management of this species

Otolith shape variability and associated body growth differences in giant grenadier, Albatrossia pectoralis.

Fish stocks can be defined by differences in their distribution, life history, and genetics. Managing fish based on stock structure is integral to successful management of a species because fishing may affect stocks disproportionately. Genetic and environmental differences can affect the shape and growth of otoliths and these differences may be indicative of stock structure. To investigate the potential for speciation or stock structure in giant grenadier, Albatrossia pectoralis, we quantified the shape of female giant grenadier otoliths and compared body growth rates for fish with three otolith shapes; shape types were classified visually by an experienced giant grenadier age reader, and were not defined by known distribution or life history differences. We found extreme variation in otolith shape among individuals; however, the shapes were a gradation and not clearly defined into three groups. The two more extreme shapes, visually defined as "hatchet" and "comb", were discernable based on principal component analyses of elliptical Fourier descriptors, and the "mixed" shape overlapped both of the extreme shapes. Fish with hatchet-shaped otoliths grew faster than fish with comb-shaped otoliths. A genetic test (cytochrome c oxidase 1 used by the Fish Barcode of Life Initiative) showed almost no variability among samples, indicating that the samples were all from one species. The lack of young specimens makes it difficult to link otolith shape and growth difference to life history. In addition, shape could not be correlated with adult movement patterns because giant grenadiers experience 100% mortality after capture and, therefore, cannot be tagged and released. Despite these limitations, the link between body growth and otolith shape indicates measurable differences that deserve more study

Number (N), average age, and age range (in parenthesis) of giant grenadier by sampling station and year used in elliptical Fourier shape analyses.

<p>Samples were either collected in the eastern Bering Sea (EBS), central Gulf of Alaska (CGOA), or the eastern Gulf of Alaska (EGOA). NA indicates that an age range is not applicable because there was one sample.</p

Total number (N), average age, and age range (in parenthesis) of giant grenadier by sampling station and year.

<p>Samples were either collected in the central Gulf of Alaska (CGOA), eastern Gulf of Alaska (EGOA), and the eastern Bering Sea (EBS). NA indicates that an age range is not applicable because there was one sample.</p

Histograms displaying the frequency for six morphometric measurements from giant grenadier for each shape: Hatchet, comb, and mixed.

<p>Histograms displaying the frequency for six morphometric measurements from giant grenadier for each shape: Hatchet, comb, and mixed.</p

Mean shapes for comb-, mixed-, and hatchet-shaped otoliths for female giant grenadier.

<p>Mean shapes for comb-, mixed-, and hatchet-shaped otoliths for female giant grenadier.</p