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Marine Ecology & Stock Assessment Program

Maternal Age Effects on Larval Viability - Southeast Alaska Rockfish

Rockfish larvae contain an oil globule at parturition (birth) that contains energy for growth and metabolic needs during the critical stage when larvae are first learning to feed. The survival rate is related to the size of this oil globule, and the size of the oil globule may be related to the age of the mother, as has been shown in some species of rockfish off the coast of California. If older rockfish mothers have more fit offspring than younger mothers, stock assessments need to reflect this difference in recruitment.

Our objectives were to collect pregnant quillback rockfish (Sebastes maliger) in Southeast Alaska and measure the oil globules based on photographs of their developing larvae. There are no published studies on effects of maternal age on larval energy reserves for rockfish species in Alaska, so our goal was to determine if maternal age affects species that occur farther north, and if so, to what degree. Quillback rockfish were chosen because they are abundant and easy to capture inshore in Southeast Alaska. Because this species lives in relatively deep water, it is an ideal prototype for honing our methodologies for other species of rockfish that live in deep, offshore waters.

Since 2006, we have collected 100 pregnant quillback rockfish. Photographs of fresh larvae were taken in the field for measurements of oil globules, and otoliths from adults were collected and are being aged by the Alaska Fisheries Science Centerís (AFSC) Age and Growth Program in Seattle.

Larvae collected in 2006 were analyzed for their protein, lipid, and water content as well as their fatty acid concentrations; a manuscript summarizing this work is in review. Because larvae from different females are at various stages of development, the developmental stage will be a covariate in future analyses. To try to bypass this obstacle, we transported live females to ABLís wet lab in April 2008 and collected embryos after they were extruded naturally for measurements of oil globules. After the larvae were extruded, they were held in tanks to determine how long they would live using only their oil globule as an energy source. Also while the larvae were developing in the lab, oil globule measurements were taken at various developmental stages to examine the decrease in oil globule size through development.

Embryos and maternal muscle tissue samples were also collected to determine if there is multiple paternity in quillback rockfish. Multiple paternity may be a way of maximizing diversity to attempt a better chance of at least a portion of a femaleís offspring surviving in a variety of environmental conditions. Some laboratory studies have found multiple paternity in rockfish, indicating that females can spawn with and store sperm from multiple males. We have the opportunity to examine multiple paternity rates in the field in quillback rockfish. Because all the females for this project will be aged, we will also be able to correlate female age with a multiple paternity strategy.

By Cara Rodgveller

Competition for Hooks on the AFSC Longline Survey

Catch rates from longline surveys are used as indices of abundance for many fish species. Relative abundance estimates from longline surveys do not usually account for possible effects of gear saturation, which potentially creates competition among fish for baited hooks and may affect estimates of changes in abundance. Scientists at ABL 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 AFSC longline surveys in Alaska waters for evidence of competition for hooks.

Sablefish and giant grenadier catch rates were negatively correlated in all six sablefish management areas (Bering Sea, Aleutian Islands, Western Gulf of Alaska, Central Gulf of Alaska, West Yakutat, and East Yakutat/Southeast Outside), and sablefish and rockfish were negatively correlated in five of the six areas (all areas except Aleutian Islands). This indicates that there is likely competition for hooks on the AFSC longline surveys. Because sablefish are mobile and aggressive predators, they are likely outcompeting grenadier and rockfish for baited hooks. Competition may be affecting grenadier and rockfish catch rates when sablefish catch rates are high.

Comparative analyses were done for AFSC trawl survey catch rates and no negative correlations were observed, indicating that the negative correlations on AFSC longline surveys are not due to differing habitat preferences or direct competition, but more likely can be attributed to competition for hooks. Available adjustments for hook competition may be biased if the probability of capture does not decrease linearly with baited hooks. A better understanding of each fish speciesí catch probabilities on longline gear is needed before adjustments for hook competition can be made.

By Cara Rodgveller

Juvenile Sablefish Tagging

Scientists from ABL have tagged juvenile sablefish in St. John Baptist Bay, near Sitka, Alaska, annually since 1986. Many of these sablefish have been recovered thousands of miles away from their initial release. These tag recoveries have greatly aided in understanding the life history of sablefish. Recently, archival tags were implanted in juvenile sablefish in St. John Baptist Bay (406 total since 2003), and the first two were recovered from the commercial fishery in 2008. These archival tags record depth and temperature over time and should give us much more information on the transitional migration of juvenile sablefish offshore to adult habitat.

The juvenile sablefish tagging cruise for 2008 took place on the NOAA ship John N. Cobb in St. John Baptist Bay 14-20 May. The goal of the cruise was to tag and release as many juvenile sablefish with Floy (spaghetti) tags as possible. An ancillary project for the NOAA aquaculture program was to freeze twelve 1-year-old and twelve 2-year-old juvenile sablefish. A total of 249 juvenile sablefish were caught, and 237 were tagged and released in St John Baptist Bay over 5 days (15-19 May) with 295 rod hours of fishing effort. Total catch-per-unit-effort equaled 0.84 sablefish per rod hour fished. Juvenile sablefish ranged in size from approximately 22 to 34 cm fork length.

By Dana Hanselman

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