Richard J. Beamish

A critical size and period hypothesis to explain natural regulation of salmon abundance and the linkage to climate and climate change

Abstract We hypothesise that salmon year class strength is determined in two stages during the first year in the ocean. There is an early natural mortality that is mostly related to predation, which is followed by a physiologically-based mortality. Juvenile salmon that fail to reach a critical size by the end of their first marine summer do not survive the following winter. In this study we describe our initial tests of this critical size and critical period hypothesis using data from ocean surveys of juvenile salmon and from experimental feeding studies on coho. Conservative swept volume abundance estimates for juvenile coho, and possibly chinook, indicate that there is high mortality in fall and winter during their first year in the sea. Studies of otolith weight show that the length and otolith-weight relationship for young coho changes in the early fall of their first ocean year. Studies of growth and associated hormone levels in feeding studies show that slow growing juvenile coho are stunted and deficient in an insulin-like growth factor-I (IGF-I). Juvenile coho sampled in September had low IGF-I values, indicative of poor growth. The results of these studies provide evidence for the general hypothesis that growth-related mortality occurs late in the first marine year and may be important in determining the strength of the year class (brood year). The link between total mortality and climate could be operating via the availability of nutrients regulating the food supply and hence competition for food (i.e. bottom–up regulation).

Have there been recent changes in climate? Ask the fish

Abstract It is generally accepted that a climate shift occurred about 1977 that affected the dynamics of North Pacific marine ecosystems. Agreement on the possibility of further climate shifts in 1989 and the late 1990s is yet to be achieved. However, there have been changes in the dynamics of key commercial fishes that indicate changes in their environment occurred in the early 1990s, and possibly around 1998. One method of measuring climate change is to observe the dynamics of species that could be affected. Several studies have described decadal-scale changes in North Pacific climate–ocean conditions. Generally, these studies focus on a single index. Using principal components analysis, we use a composite index based on three aspects of climate ocean conditions: the Aleutian Low Pressure Index, the Pacific Atmospheric Circulation Index and the Pacific Interdecadal Oscillation Index. We link this composite index (Atmospheric Forcing Index) to decadal-scale changes in British Columbia salmon and other fish populations. Around 1989 there was a change from intense Aleutian Lows (above average south-westerly and westerly circulation patterns and warming of coastal sea surface temperatures) to average Aleutian Lows (less frequent south-westerly and westerly circulation and slightly cooler coastal sea surface temperatures in winter). These climate–ocean changes were associated with changes in the abundance and ocean survival of salmon (Oncorhynchus spp.), distribution and spawning behaviour of hake (Merluccius productus) and sardines (Sardinops sagax) and in recruitment patterns of several groundfish species.

Acidification of lakes in Canada by acid precipitation and the resulting effects on fishes

In the Sudbury region of Ontario, Canada, fallout of sulfur oxides has been shown to be responsible for damage to vegetation, lakes and fishes.The acidic fallout has been shown to effect a rate of acidification in many lakes that over several decades has resulted in the extinction of many species of fishes. Fish exhibit profound differences in acid tolerance but show some similarities in their physiological response to levels within the range of their individual susceptibilities. Prior to extinction most females of a particular species did not release their ova to be fertilized. The failure of females to spawn was coincident with an inability to maintain normal serum Ca levels. In some species growth was reduced despite an adequate supply of preferred food items. High concentrations of acid were considered to be the principal factor stressing the fish populations. Elevated concentrations of some heavy metals may add to the stress caused by high concentrations of acid.

General effects of climate change on Arctic fishes and fish populations.

Abstract Projected shifts in climate forcing variables such as temperature and precipitation are of great relevance to arctic freshwater ecosystems and biota. These will result in many direct and indirect effects upon the ecosystems and fish present therein. Shifts projected for fish populations will range from positive to negative in overall effect, differ among species and also among populations within species depending upon their biology and tolerances, and will be integrated by the fish within their local aquascapes. This results in a wide range of future possibilities for arctic freshwater and diadromous fishes. Owing to a dearth of basic knowledge regarding fish biology and habitat interactions in the north, complicated by scaling issues and uncertainty in future climate projections, only qualitative scenarios can be developed in most cases. This limits preparedness to meet challenges of climate change in the Arctic with respect to fish and fisheries.

Loss of fish populations from unexploited remote lakes in Ontario, Canada as a consequence of atmospheric fallout of acid

Abstract Fish populations in the study lakes were disappearing, primarily as a result of the high acid content of the lakes. As a lake became acidic, the more acid sensitive species ceased reproduction and eventually disappeared. The loss of fish populations resulted both from a long-term lethal effect and from an absence of recruitment of young into the population due to the failure of reproduction. In one of the lakes the acid levels have been high long enough to cause the loss of populations of even the most resistant species. The anomalous concentrations of nickel in the lakes and precipitation; the high concentrations of nickel emitted into the atmosphere in Sudbury, Ontario; the ability of sulfur dioxide to form acid in the atmosphere and fallout in the precipitation over considerable distances from the emission source; the tremendous quantities of sulfur dioxide emitted by industry in Sudbury; the abnormally high concentrations of hydrogen and sulfate ions in the study lakes; all indicated that the emissions from the nickel smelters near Sudbury were the most probable source of contamination that has resulted in the loss of fish stocks from O.S.A., Muriel, and other lakes.

An Overview of Effects of Climate Change on Selected Arctic Freshwater and Anadromous Fishes

Abstract Arctic freshwater and diadromous fish species will respond to the various effects of climate change in many ways. For wide-ranging species, many of which are key components of northern aquatic ecosystems and fisheries, there is a large range of possible responses due to inter- and intra-specific variation, differences in the effects of climate drivers within ACIA regions, and differences in drivers among regions. All this diversity, coupled with limited understanding of fish responses to climate parameters generally, permits enumeration only of a range of possible responses which are developed here for selected important fishes. Accordingly, in-depth examination is required of possible effects within species within ACIA regions, as well as comparative studies across regions. Two particularly important species (Arctic char and Atlantic salmon) are examined as case studies to provide background for such studies.

Spiny Dogfish Predation on Chinook and Coho Salmon and the Potential Effects on Hatchery-Produced Salmon

Abstract -Large numbers of spiny dogfish Squalus acanthias moved into the area near the mouth of the Big Qualicum River, British Columbia, at the time hatchery-reared smolts of Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch were leaving the river in 1988 and 1989. A small percentage of the spiny dogfish preyed on the smolts, but the resulting smolt mortality is believed to have been large because of the large numbers of spiny dogfish in this area. Spiny dogfish also fed on adult salmon in the fall. The long-term decline in survival of chinook salmon produced at the Big Qualicum Hatchery was similar to the pattern of survival of other hatchery-produced salmon. We propose that this long-term decline in survival results from predation.

Use of Fin-Ray Sections to Age Walleye Pollock, Pacific Cod, and Albacore, and the Importance of this Method

Abstract Thin sections of fin rays were used to estimate the age of walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), and albacore (Thunnus alalunga). Because the number of methods of determining the age of fishes is limited, it is advisable that investigators develop a facility for the fin-ray method so that the best aging method for a stock of fish can be selected. Use of several methods also helps in estimating the accuracy of age determinations in the absence of a validation procedure that is applicable to all age-groups in a population.

Ontogenetic Diet Shifts of Juvenile Chinook Salmon in Nearshore and Offshore Habitats of Puget Sound

Abstract Marine growth and survival of juvenile Chinook salmon Oncorhynchus tshawytscha depend in part on the quality and quantity of prey consumed during this potentially critical life stage; however, little is known about the early marine diet of these fish or factors that affect the diets variability. We examined the recent (2001–2007) dietary habits of Puget Sound, Washington, Chinook salmon (listed as threatened under the U.S. Endangered Species Act) during their first marine growing season (April–September). Juvenile Chinook salmon initially fed in nearshore marine habitats and then shifted to feed primarily offshore during July–September. Diet composition varied significantly among sampling regions (northern, central, and southern), habitats (nearshore, offshore), years, months, and fish size-classes. At nearshore sites, insects (all months) and gammarid amphipods (July) were dominant prey sources, whereas in offshore diets decapods (primarily crab larvae; July) and fish (September) were most impo...

The re-occurrence of sardines off British Columbia characterises the dynamic nature of regimes

Sardine (Sardinops sagax) fisheries were the largest in British Columbia from the mid-1920s to the mid-1940s, and catches averaged 40,000t annually. In 1947 not only did the fishery off British Columbia collapse but also the sardines disappeared totally from British Columbia waters. Sardines re-appeared in 1992, after a period of 45 years. As their abundance increased, sardines spawned off the west coast of British Columbia in 1997 and 1998, and one year old juveniles became distributed along the entire coast and off the coast of Alaska. This distribution and spawning behaviour was not reported in the 1930s and 1940s. The changes in sardine dynamics were related to regime shifts, but did not oscillate in synchrony with all the decadal-scale changes in climate as indexed by the pattern of the Atmospheric Forcing Index (AFI). This response indicates that the linkage between sardines and climate regimes is specific to an assemblage of factors that characterise the regimes. Indicators of ecosystem change such as temperature should be viewed more as surrogates of change than specific regulators of distribution and abundance. The specific aggregate of factors that create favourable ecosystems for sardines remains to be discovered. We suggest that it is the change of regimes that creates conditions favourable to sardines by improving the productivity of diatoms that are specific to the improved early survival of larval sardines.