Secondary sexual characters, energy use, senescence, and the cost of reproduction in sockeye salmon

Abstract

Reproductive development and energy stores were characterized for sockeye salmon (Oncorhynchus nerka) maturing in the wild (Pick Creek, Bristol Bay, Alaska). Between freshwater entry and the start of spawning, ovaries increased in mass by 87.1% and secondary sexual characters increased in linear dimension by 13.0-47.4%. Between the start of spawning and death, secondary sexual characters decreased in relative size by 3.3-12.7%. Mass-specific somatic energy declined from freshwater entry (6.7% fat, 20.6% protein, 6.6 kJ·g-1) to the start of spawning (1.6% fat, 18.0% protein, 4.5 kJ·g-1) and finally to death (0.1% fat, 14.4% protein, 2.9 kJ·g-1). Stored fat appeared to be used primarily for upriver migration and egg production, whereas stored protein appeared to be used primarily for the development of secondary sexual characters and metabolism during spawning. Most development of secondary sexual characters occurred late in maturation, perhaps to forestall deterioration of muscle tissue. Relative to populations with long freshwater migrations, Bristol Bay sockeye salmon stored less fat before entering fresh water and used less fat before death. The total energy cost of reproduction (freshwater entry until death, including gonad investment) was 74.1% for females and 66.1% for males, higher than levels typically reported for iteroparous salmonids.

Energy content of Pacific salmon as prey of northern and southern resident killer whales

“…Previous studies have documented the importance of fish size and lipid content in determining the energy content of salmon (Gilhousen 1980, Brett 1995, Hendry & Berg 1999, but ours is the first comprehensive assessment of Salmon kilocalorie levels are derived mostly from lipids and proteins, because carbohydrates constitute < 0.5% of the somatic tissue of salmonids (Jonsson et al 1991(Jonsson et al , 1997. Variation in energy density among salmon species and populations is almost entirely determined by the degree to which they store lipids, because the protein content, structurally important in muscle development and swimming performance, varies little among mature fish (Brett 1995, Hendry & Berg 1999. Accordingly, the energy density among salmon species and among Chinook salmon populations was highly correlated with lipid content (Figs.…”

“…3a & 5a, respectively). As salmon mature and migrate upriver, they first burn fat to provide energy for migration and egg development, conserving protein for the subsequent development of secondary sexual characteristics (Hendry & Berg 1999 ) associated with fish length (fork length, mm) using ln-transformed values [ln kcal = (slope coefficient × ln MCL) + intercept coefficient], where MCL is mean composite fish length). The 'full model' regression is the best fit for all 7 Chinook salmon population-complexes sampled (Skeena River, Fraser River, Columbia River fall run, Columbia River spring run, Puget Sound, Puget Sound blackmouth, and Sacramento River).…”

“…The lower lipid contents of the Chinook salmon from Puget Sound and Columbia River fall run fish sampled for this study (mostly lower river stocks) are likely due to the short distances they migrate upstream to spawn. Some of the variation in lipid content among Chinook salmon populations may also be associated with their advancing maturation state, as lipid content declines dramatically as fish move into freshwater and become sexually mature (Shearer et al 1994, Ewald et al 1998, Hendry & Berg 1999. For example, the difference in lipid content between immature (9.9%) and mature in-river-caught fish (6.1%) from Puget Sound suggests that the mature fish had started to metabolize their fat reserves for reproduction when sampled.…”

Depth variation in isotopic composition of benthic resources and assessment of sculpin feeding patterns in an oligotrophic Alaskan lake

“…The amount of energy consumed and stored in a freshwater fish is related to overwinter survival (Gardiner and Geddes 1980;Meyer and Griffith 1997) and subsequent reproduction (Meffe and Snelson 1993). Salmon eggs are a valuable resource to freshwater fish that are abundant, high in fat content (Hendry and Berg 1999), and conveniently available for consumption directly prior to winter in coastal freshwater systems in Alaska. Our data suggest that sculpins likely rely on deep benthic resources in addition to the seasonal subsidy of salmon-derived resources.…”

Breeding site selection by coho salmon (Oncorhynchus kisutch) in relation to large wood additions and factors that influence reproductive success

“…Reproduction is not possible for adults that do not survive through nest construction, oviposition, and egg covering phases of breeding, and it is reasonable to predict that breeding sites should be linked to instream features such as cover that can reduce the susceptibility of adults to predation (Hendry and Berg 1999;Hendry et al 2001). Such habitats that promote survival during redd (nest) construction may be limited in their availability, sometimes leading to aggregations and intense competition among females for breeding sites (Van den Berghe and Gross 1989;Fleming and Gross 1994).…”