Feeding of larval walleye pollock (Theragra chalcogramma) in the oceanic domain of the Bering Sea

Thesis (M.S.) University of Alaska Fairbanks, 1994Feeding of larval walleye pollock was examined with respect to abundance and distribution of prey at six depths in the oceanic domain of the Bering Sea in April 1992. Walleye pollock larvae and copepod nauplii distribution peaked at 30 m depth. Among copepod nauplii, walleye pollock larvae selected for Metridia sp. and Microcalanus sp., but against Oithona similis, even though the latter were the most abundant prey taxon. In addition, the larvae selected for larger nauplii and tended to consume stages I and II Oithona similis and stages lll-V calanoid nauplii. Larvae at 30 m depth had the highest incidence of feeding and number of prey items ingested. Although the 30 m depth stratum provided best physical and foraging conditions, the overall low percentage of feeding larvae and low numbers of prey consumed, suggest that foraging conditions for larval walleye pollock at the time of sampling were below saturation feeding levels

Timing and duration of mating and brooding periods of Atka mackerel (Pleurogrammus monopterygius) in the North Pacific Ocean

The timing and duration of the reproductive cycle of Atka mackerel (Pleurogrammus monopterygius) was validated by using observations from time-lapse video and data from archival tags, and the start, peak, and end of spawning and hatching were determined from an incubation model with aged egg samples and empirical incubation times ranging from 44 days at a water temperature of 9.85°C to 100 days at 3.89°C. From June to July, males ceased diel vertical movements, aggregated in nesting colonies, and established territories. Spawning began in late July, ended in mid-October, and peaked in early September. The male egg-brooding period that followed continued from late November to mid-January and duration was highly dependent on embryonic development as affected by ambient water temperature. Males exhibited brooding behavior for protracted periods at water depths from 23 to 117 m where average daily water temperatures ranged from 4.0° to 6.2°C. Knowledge about the timing of the reproductive cycle provides a framework for conserving Atka mackerel populations and investigating the physical and biological processes influencing recruitment

Effects of Maternal Growth on Fecundity and Egg Quality of Wild and Captive Atka Mackerel

Trade-offs in energy allocation between growth and reproduction can result in variations in reproductive potential in fish with differing growth patterns. Spawning biomass is often used as a proxy for reproductive potential on the assumption that fecundity is directly proportional to body weight. We examined variations in the reproductive potential of Atka mackerel Pleurogrammus monopterygius by studying the effect of differential growth and condition patterns on fecundity, atresia, and egg energy. Fecundity and egg energy were determined for fish from two geographic areas, Seguam Pass and Amchitka Island, Alaska, and compared with those of fish held in captivity. These Atka mackerel showed distinct differences in growth and condition, with weight at length and length at age being the highest among captive fish, intermediate among fish from Seguam Pass, and lowest among fish from Amchitka Island. Realized fecundity showed that on average captive fish spawned seven batches, fish from Seguam Pass six batches, and fish from Amchitka Island five batches. For wild fish, potential and realized fecundity at length or age was significantly higher at Seguam Pass than at Amchitka Island, whereas the fecundity-at-weight relationship did not differ by area, suggesting that weight is a better predictor of fecundity than length or age. Atresia and batch fecundity by length or weight did not differ by area, suggesting that the variation in fecundity is better explained by the variation in batch number than by batch size. Oocyte dry weight was higher for captive fish than for wild fish, whereas batch order did not significantly affect oocyte dry weight. Increased potential fecundity, realized fecundity, and oocyte quality in Atka mackerel females were strongly related to body size, indicating that growth differences and maternal feeding success impact the fecundity and oocyte quality of Atka mackerel. Therefore, changes in growth and condition patterns need to be taken into account to accurately estimate the reproductive potential of this species

Plant protein-based feeds and commercial feed enable isotopic tracking of aquaculture emissions into marine macrozoobenthic bioindicator species

<p>Brittle stars (<i>Ophiura</i> spp.) and other benthic macrofauna were collected in a prospective mariculture area in the North Sea to determine if these taxa could be used as indicator species to track nutrients released from future offshore aquaculture sites. We analysed natural carbon and nitrogen stable isotopic signatures in tissues from macrofauna and compared these to six feed ingredients and four experimental diets made thereof, as well as to a commercial feed with and without lipid and carbonate removal. Our data suggest practicability of using isotopic signatures of <i>Ophiura</i> spp. to track aquaculture-derived organic material if plant-based fish diet ingredients and commercial feed were used for fish farming in the German Exclusive Economic Zone. Diets with high fish meal content would not be detected in <i>Ophiura</i> spp. using isotopic measures due to the similarity with the marine background. Our data provide valuable baseline information for studies on the impact of offshore aquaculture on the marine environment.</p

The effect of different fish feed compositions on δ¹³C and δ¹⁵N signatures of sea bass and its potential value for tracking mariculture-derived nutrients

<p>Increasing demand for fish and seafood calls for an expansion of aquaculture production. At the same time, the status of the marine environment must not be jeopardised. Stable isotopes are potential markers for tracking feed-based nutrient flows from aquaculture into marine biota. Here, we demonstrate how four experimental diets (main protein components: fishmeal, soya protein concentrate, wheat gluten, and <i>Jatropha</i> kernel meal) and a commercial diet induce characteristic δ¹³C and δ¹⁵N signals in sea bass (<i>Dicentrarchus labrax</i>) during nine weeks of laboratory feeding under replicate conditions. The plant-protein-based diets containing wheat gluten and soya, and the commercial feed consistently induced the largest isotopic differentiation of the fish, both from the feed source and from the pre-experimental condition. The large difference of the fish on plant-protein-based diets compared to the range of natural isotopic variation in the macrozoobenthos of the North Sea lends support to the idea that plant-based feeds are suitable for tracing mariculture-derived organic matter under practical conditions. The commercial feed had a similar effect as the experimental feeds and would be a cost-effective option for an offshore aquaculture experiment.</p