Fisheries bycatch as an inadvertent human-induced evolutionary mechanism

Abstract

Selective harvesting of animals by humans can affect the sustainability and genetics of their wild populations. Bycatch - the accidental catch of non-target species - spans the spectrum of marine fauna and constitutes a harvesting pressure. Individual differences in attraction to fishing vessels and consequent susceptibility to bycatch exist, but few studies integrate this individual heterogeneity with demography. Here, we tested for the evidence and consequences of individual heterogeneity on the demography of the wandering albatross, a seabird heavily affected by fisheries bycatch. We found strong evidence for heterogeneity in survival with one group of individuals having a 5.2% lower annual survival probability than another group, and a decrease in the proportion of those individuals with the lowest survival in the population coinciding with a 7.5 fold increase in fishing effort in the foraging areas. Potential causes for the heterogeneity in survival are discussed and we suggest that bycatch removed a large proportion of individuals attracted by fishing vessels and had significant phenotypic and population consequences.

Figure 1. Changes in the proportion of newly encountered individuals (successful breeders) from category 1 in the population of wandering albatrosses from Possession Island between 1960 and 2010.

Parameter estimates are from Model 2. Errors bars are 95% confidence intervals.

Figure 2. Proportion of newly encountered individuals (successful breeders) from category 1 and longline fishing effort.

Changes in (a) the proportions of category 1 individuals in the population of wandering albatrosses from Possession Island between 1960 and 2010, as a function of longline fishing effort south of 30°S in the Indian Ocean; and (b) the annual estimated longline fishing effort south of 30°S in the Indian Ocean for the Japanese and Taiwanese fisheries combined. Parameter estimates in (a) are from Model 2. Light grey, dark grey and black coding correspond to time periods of low, increasing and decreasing fishing effort.

Figure 3. Numbers of breeding pairs of wandering albatrosses at Possession Island, from 1968 to 2008.

Black dots indicate observed counts (error bars are ± SE), grey line indicates numbers predicted by a matrix population model without heterogeneity on adult survival, and black line indicates numbers predicted by a matrix population model with heterogeneity on adult survival.