Gordon A. McFarlane

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.

Estimating the Abundance of Juvenile Coho Salmon in the Strait of Georgia by Means of Surface Trawls

Abstract A fixed survey design with a randomized depth component and a large rope trawl that fished surface waters at a speed of approximately 5 knots was used to estimate the abundance of juvenile coho salmon Oncorhynchus kisutch in the Strait of Georgia. The estimates of 4.2 million juveniles in September 1996, 3.0 million in September 1997, and 3.0 million in September 1998 were minimal because the catchability of the net was probably lower than that used in the analysis. In 1997, by using hatchery-marking percentages, we estimated that 3.4 million wild coho salmon smolts entered the Strait of Georgia from Canadian rivers. The estimates of juvenile abundance made in September 1997 were considerably larger than the estimated total returns in 1998, indicating that the marine mortality in fall and winter is an important component of the total marine mortality determining the final strength of the brood year. The use of surveys for estimating juvenile coho salmon abundance is a contribution to the understa...

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.

Age and length at maturity of the female spiny dogfish,Squalus acanthias, in the Strait of Georgia, British Columbia, Canada

SynopsisA total of 3068 female spiny dogfish were examined to determine the age and length at maturity. The median age at maturity for females was 35.5 years with 95% confidence limits between 35.0 and 35.9 years. It was found that slower growing dogfish tended to mature at a smaller size. A deterministic model incorporating fecundity, growth and reproduction was used to examine the reproductive style of spiny dogfish. The age at maturity reported corresponds to the level that theoretically maximizes lifetime reproductive output for a cohort.

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.

Movements and Mortality of Tagged Male and Female Lingeod in the Strait of Georgia, British Columbia

Abstract Using mark-recovery data obtained from 1982 to 1987, we estimated rates of dispersal from release locations and mortality for mature male and female lingcod Ophiodon elongatus in the Strait of Georgia, British Columbia. Under the assumption of random dispersal from release locations, and incorporating sport-fishery effort data obtained by an independent creel survey, we determined from sport-fishery tag recoveries that male lingcod dispersed at a mean rate of 500 m/d (95% confidence interval, 400–600 m/d) and females dispersed at 1,040 m/d (900–1,180 m/d). In an unbounded environment, this can be interpreted as 95% of tagged males remaining within 17 km and 95% of females within 34 km of the release location after 1 year at large, In the confines of the Strait of Georgia, actual dispersal would be less. Males dispersed significantly (P < 0.01) more slowly than females, and they had a higher annual instantaneous total (fishing plus natural) mortality rate (95% confidence intervals 0.72–1.25 for ma...

Incorporating the dynamics of marine systems into the stock assessment and management of sablefish

Progress in ecosystem management requires the characterisation of the dynamics of a species’s ecosystem and the influences of climatic oscillations on those dynamics. Within the North Pacific, ecosystem dynamics have been described on decadal-scales (regimes) and have been shown to shift abruptly (regime shifts). The year class success of sablefish ( Anoplopoma fimbria ) exhibit decadal-scale patterns that relate to decadal-scale patterns in North Pacific climate–ocean conditions. As an example, and a step towards, incorporating the dynamics of marine systems into the stock assessment and management of sablefish, we produce a ‘report card’ that characterises the species’s ecosystem on decadal-scales. This report card consists of a matrix of climatological and oceanographic indices for the North Pacific, and regional environmental and biological indices. It indicates that both Pacific-wide and regionally, conditions were generally good for sablefish year class strength during the 1977–1988 regime, but these favourable conditions did not persist into the 1990s. Exploitation scenarios can be developed around the decadal-scale dynamics in sablefish year class success and their life history, in particular longevity. Fisheries managers can begin to develop exploitation strategies that acknowledge these changes in the sablefish ecosystem. The report card presents an aggregation of parameters that, on average, gives an impression of productivity during a specific regime and can be used to augment present stock assessment and management efforts.  2001 Elsevier Science Ltd. All rights reserved.

Shifts in fisheries management: adapting to regime shifts

For many years, fisheries management was based on optimizing yield and maintaining a target biomass, with little regard given to low-frequency environmental forcing. However, this policy was often unsuccessful. In the last two to three decades, fisheries science and management have undergone a shift towards balancing sustainable yield with conservation, with the goal of including ecosystem considerations in decision-making frameworks. Scientific understanding of low-frequency climate–ocean variability, which is manifested as ecosystem regime shifts and states, has led to attempts to incorporate these shifts and states into fisheries assessment and management. To date, operationalizing these attempts to provide tactical advice has met with limited success. We review efforts to incorporate regime shifts and states into the assessment and management of fisheries resources, propose directions for future investigation and outline a potential framework to include regime shifts and changes in ecosystem states into fisheries management.

Growth Analysis of Strait of Georgia Lingcod by Use of Length-Frequency and Length-Increment Data in Combination

Abstract We estimated von Bertalanffy growth parameters for male and female lingcod Ophiodon elongatus in the Strait of Georgia, British Columbia, by use of length-frequency and length-increment data in combination. Although length frequencies can be an inferior data set if the overlap of year-classes obscures the modal structure, length-frequency data together with length-increment data provided a useful data set for analyzing lingcod growth. For determining growth and growth variance, length-frequency data were more useful for the younger year-classes, whereas length-increment data were more informative for older individuals. We used and extended Sainsburys formulation of the von Bertalanffy growth model to incorporate a sinusoidal cycle of annual growth because we recognized such a pattern in our length-increment data. We concluded that male lingcod grew more slowly than female lingcod in the Strait of Georgia, and that the growth rates for both males and females were slower than rates determined from...

A Tag Suitable for Assessing Long-Term Movements of Spiny Dogfish and Preliminary Results from Use of This Tag

Abstract A tag was developed and tested for the long-term marking of spiny dogfish (Squalus acanthias). The tag is retained without corrosion and with minor skin abrasion. They have not been lost from fish held in captivity for up to 3 years. Most recoveries were in the immediate release area, but some fish were recovered 250 to 7,000 km from the release area. The greatest distance travelled (7,000 km) was by a fish tagged in June 1980 in Queen Charlotte Sound and recovered in November 1982 off the northeast coast of Japan. The recovery rate for fish tagged and released in the Strait of Georgia and standardized for catch suggested that movement of spiny dogfish throughout their range is an important aspect of their biology. Less movement was exhibited by fish tagged in the Hecate Strait region. However, of the fish that did move, the majority were recaptured off Washington and the west coast of Vancouver Island and not in the Strait of Georgia.