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Recovery Strategy for three Wolffish: Northern, Spotted & Atlantic (Proposed) 2007

4. Biological Limiting Factors

Basedon observed growth and fecundity of A. lupus in USA waters, Musick (1999) described the reproductive productivity of wolffish as “low”. The testes of these species are relatively small, sperm and egg production is low, fertilization is internal and eggs and larvae are large. Although fecundity is low, internal fertilization (Pavlov 1994), nesting habits and egg guarding behaviour in A. lupus (Keats et al. 1985) effectively increases potential for survival of individuals during the early life stages.

Many demersal fish species in the eastern Canadian waters have undergone similar changes in distribution and population decline over the same time period, but there is little consensus in the literature as to the proximal cause for these multi-species declines. The patterned declines and the contraction of distributions to deeper waters observed with wolffish have also been observed in other species during the same time period (Atkinson 1994, Kulka et al. 1995).

Attempts to relate changes in population size and distribution to environmental signals have met with little success. As well, over-fishing hypotheses have not been fully satisfactory in many instances in explaining the declines. Although bycatch mortality clearly has contributed to the declines, evidence of over-fishing as the proximal cause is lacking for non-commercial species (Simpson and Kulka 2002). For wolffish, the greatest declines occurred where fishing effort was low and the remaining concentrations largely coincide with the most heavily fished areas (Kulka and Simpson 2004). Future research may reveal the importance of environmental factors in the decline.

In addition to the problem of estimating the status of populations arising from incomplete coverage of the population range, the relatively short period that standard stratified random fall surveys have been done (1977 to present) is not sufficiently long to provide information on long term trends for these long lived species. Marine fish undergo natural fluctuations often resulting from variable recruitment and thus peaks and valleys over the long term are the norm. Fluctuating trends are apparent for virtually all monitored species. To pick a point in time when a population is at its peak and compare it to the low point in the trend may not be a valid measure of endangerment with extinction. Not enough is known about the long term population trends of these species, or the environmental influences to fully understand how critical the abundance levels reached in the mid-1990s are to the survival of the species in Canadian waters. However, for species, even at their lowest abundance still numbering in the multi-millions, during a time when the environment was apparently unfavourable (Atkinson 1994), it seems unlikely that biological extinction is an immediate issue.

Fishing pressure accentuates the downward component of fluctuations caused by natural influences even when the exploitation rate is relatively low. How much of the precipitous declines observed between the early 1980s and the mid-1990s is attributable to natural fluctuation and how much is an anomalous event caused by extraordinary circumstances (natural or anthropogenic, or both) is unknown. Nonetheless, attention must be paid to the declining biomass trends and the reduction in extent of the distribution in the 1980s and 1990s, particularly in the north.

If the survey time series for A. minor were only available from 1994, the conclusion in 2001 would be that this species nearly tripled in abundance and is at the highest value in the time series in 2001. Similarly, the 1997-1998 values could have been above average. The spring survey data on the Grand Banks going back to 1971 suggest this to be case.

The apparent increase in biomass and abundance since the mid-1990s, for A. minor and A. lupus is an encouraging sign. Whether this increase resulted from more favourable environmental conditions or reduced fishing pressure in the 1990s, or a combination of effects is unclear. However, several additional years of research survey data are required to confirm whether recovery is taking place. Furthermore, with any apparent increase in biomass, it seems likely that the extent of the wolffish distributions would also increase within the range previously observed in the absence of an environmental shift that might prevent a re-colonization (Simpson and Kulka 2002).