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Benoît, H. P., Plante, S., Kroiz, M., and Hurlbut, T. 2013. A comparative analysis of marine fish species susceptibilities to discard mortality: effects of environmental factors, individual traits, and phylogeny. – ICES Journal of Marine Science, 70:99–113. Determining the sustainability of fishing mortality for discards requires information on discard amounts as well as capture and release mortality rates. Formal estimates of these rates are costly and only available for a limited number of species and fisheries. In their absence, proxies for discard mortality could inform risk assessments of fishing mortality sustainability for discarded species. Here, time-to-mortality (TM) was assessed for 48 marine fish species exposed to air following capture during an annual multi-species bottom-trawl survey. Species-specific estimates of TM were related qualitatively to more formal estimates of discard mortality from commercial fisheries, confirming the use of TM as a proxy. The effects on TM of species and individual traits, phylogenetic similarity (proxy for traits not explicitly included in the analysis) and environmental factors related to capture were also assessed. Much of the observed individual variability was explained by intraspecific and interspecific positive relationships between body size and TM. Sedentary species and those lacking a gas bladder or deciduous scales had greater TM. Effects of phylogeny and capture depth and temperature were also found. This study demonstrates how reliable proxies of discard mortality rate can be readily obtained in the field or estimated from relevant covariates.

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Oxygen saturation levels that killed 50 and 5% of cod Gadus morhua over 96 h averaged 21·2 and 27·7%, respectively. No fish survived at 10% saturation and only a few survived at 16% saturation, whereas no mortality occurred at 34 and 40% oxygen saturation. Since metabolic rate and oxygen consumption increase with increasing temperature, we hypothesized that cod would be less tolerant to hypoxic conditions at 6 than at 2 C. However, temperature (2 and 6 C) had no measurable impact on cod survival. Small (mean ..; 45·2 4·2 cm) and large (57·5 3·8 cm) cod had the same tolerance to hypoxia. At the end of the experiments, hypoxia had a significant effect on blood haematocrit, mean cellular haemoglobin content, liver lactate, plasma glucose and plasma lactate, but accounted for only a small fraction (<10%) of the variation, except for plasma lactate which exhibited a strong response with concentrations increasing progressively with decreasing levels of oxygen saturation. Temperature had a significant effect on most variates in normoxia and hypoxia. Variates also affected by oxygen level showed significant interactions between oxygen and size or temperature effects. However, these interactions accounted for only a small proportion of the variation. Physiological parameters indicated that extending the duration of our tests beyond 96 h would not have changed our estimates of the lethal thresholds. Hypoxic conditions are a permanent feature of the deep waters of the Gulf of St Lawrence. This study shows that a significant portion of the benthic habitats in the Gulf are uninhabitable for cod which would be expected to avoid waters below 28% oxygen saturation. 1998 The Fisheries Society of the British Isles

There is a growing interest in developing either food or feed ingredients from the large volumes of Pacific Ocean perch (POP) by‐products produced in Alaska. Determining the chemical composition of POP by‐products is fundamental for developing novel ingredients using these materials. The objective of this study was to chemically characterize POP and its by‐products. Triplicate samples of fresh POP whole fish, heads, frames and viscera were obtained from a commercial seafood processor in Alaska, and each replicate sample was individually analyzed for moisture, lipid, protein, ash, amino acid and mineral contents, fatty acid profile, lipid classes, pH, protein solubility, color, volatile amines and sodium dodecyl sulfate polyacrylamide gel electrophoresis of the proteins. The lipid and protein contents of the POP samples were 7.8 and 17.9% for whole fish, 10.5 and 15.2% for frames, 9.3 and 14.9% for heads, and 13.5 and 11.3% for viscera, respectively. Frames, heads and whole fish had ash values of 6.0, 6.7 and 4.3%, respectively. From the amino acid profiles, the values for lysine ranged from a low value of 7.3% for heads to a high value of 8.3% of total amino acids for frames. Methionine values ranged from 3.2 to 3.4% for all tissues. Frames and heads had high values for calcium and phosphorus, while viscera had the highest levels of iron. The analysis of fatty acids indicated high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) with EPA/DHA ratios of approximately 2 for all tissues. Results indicated that the protein fraction of POP by‐products was of high quality, and its lipids were a valuable source of omega‐3 fatty acids. PRACTICAL APPLICATIONS This paper is the first examination of the chemical and nutritional properties of Pacific Ocean Perch (POP). There are fish processors that process substantial volumes of POP; however, the byproduct is seldom further processed into unique products. Processors could segregate POP byproducts and use this material to make products such as oils with a unique fatty acid profile as well as a distinctive color. Likewise single species POP byproduct meals could be produced and possibly fill niche market needs as food and feed ingredients.

Indices of energy reserves may represent interesting parameters that can be used as bioindicators in environmental studies. The goal of this study was to identify a water–energy model that could predict energy reserves in winter flounder Pseudopleuronectes americanus. Winter flounder kept in captivity and fed different food types (either capelin Mallotus villosus or Atlantic herring Clupea harengus, amphipods Anonyx sarsi, and wet pellets) for 2, 5, and 14 months and wild fish captured in May, July, and October were used to show a large range in energy content. High levels of correlation were observed between water and energy contents in fish carcasses (r2 = 0.82) and muscle (r2 = 0.75). However, the biochemical composition of the liver remained relatively constant, despite changes in the hepatosomatic index. The condition factor (somatic weight/length3) was associated with energy reserves (i.e., water contents), but the coefficients of determination were smaller (0.18 < r2 < 0.34). We found that muscle water content, which can easily be determined, is an efficient way to accurately predict energy reserves in winter flounder.

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The goal of this study was to determine rearing conditions that would improve the survival of broodstock of winter flounder Pleuronectes americanus. We hypothesized that keeping wild winter flounder in iso-osmotic water would reduce the energy costs related to osmoregulation; the resulting energy gain could then be used for growth or immune responses. Eighty fish were randomly separated into four tanks, two containing seawater (SW; 28.7 ± 0.9‰ (mean ± SD)) and two containing brackish water (BW; 14.7 ± 1.7‰). Fish were sampled after 2 and 5 months of captivity for evaluation of their condition and stress status. Between the second and fifth months, the condition index increased significantly in both salinity groups, whereas body water content decreased. No salinity effect in terms of growth, condition, or energy reserves was found. However, the fish in BW showed much lower mortality. We found that the fish in SW had higher levels of the physiological indicators of stress than those in BW, which could have increased the risk of opportunistic infections in the former. Also, thrombocytes were absent in the SW fish after 2 months of captivity, which may have contributed to some mortalities. The lower resistance of certain opportunistic pathogens to BW is another possible explanation as to why fish in BW had lower occurrences of infectious diseases.