Influence of population decline, fishing, and spawner variability on the recovery of marine fishes

Abstract

Based on an analysis of 90 marine fish populations, collapses (the greatest proportional reduction in spawner biomass over 15 years) are predicated typically by dramatic increases in fishing mortality and recoveries are more likely to occur when exploitation is reduced. However, among populations for which fishing mortality declined after collapse, recovery was independent of exploitation rate, even when fishing mortality (F) post-collapse was expressed as a function of each population's maximum growth rate (r). After a period of 15 years, many populations that experienced 15 year declines >60% exhibited little or no recovery, despite considerable reductions in fishing mortality. This suggests that factors other than fishing may be considerably more important to recovery, and fishing less important, than previously thought. Furthermore, among populations for which fishing mortality decreased post-collapse, rate of population decline was a reliable predictor of recovery. With the possible exception of clupeids, variation in marine fish breeding population size was found to differ little from that of other vertebrates, and such variability appears to have no effect on rate of recovery. In addition to providing an empirical framework for the study of population collapse and recovery, the analyses presented here provide a means of assessing the precautionary nature of various population-decline thresholds used to assign extinction risks to marine fish. 2001 The Fisheries Society of the British Isles

Measuring marine fish biodiversity: temporal changes in abundance, life history and demography

“…Of the remaining 18 populations, 14 inhabit waters of the North midAtlantic area, a region in which substantive increases in demersal fish biomass are indeed evident (figures 4 and 5). Notwithstanding the fact that some populations are capable of rapid recovery (as previous work clearly indicates ;Hutchings 2000Hutchings , 2001, it is unwise to use data taken primarily from a single family known for its apparent resilience (Clupeidae, which includes herrings and sardines) and from a single geographical area to draw general conclusions about the fate of collapsed marine fish.…”

“…Thus, any reduction in the rate of loss of temperate marine fish biodiversity can probably be attributed to long-overdue management actions to reduce fishing effort on targeted species (although the benefits from an ecosystem perspective may be offset if effort is simply shifted to other species). While such effort controls may be insufficient to effect substantive recovery (Hutchings 2001), they should be sufficient to reduce the rate of population decline in the absence of Allee effects.…”

A Tale on the Demersal and Bottom Dwelling Chondrichthyes in the South of Sicily through 20 Years of Scientific Survey

“…Fisheries have caused severe declines in many species, and although there are still no documented cases of complete extinction, there is considerable debate as to whether marine species could become extinct (in Refs. [2,6,7]). …”

Evaluating the biological effectiveness of fully and partially protected marine areas

“…Almost certainly, the frequency and intensity of exploitation experienced by a species in a fishery will greatly influence the magnitude of response to protection from fishing. For example, reductions in the spawning stock biomass resulting from high levels of fishing mortality, reduces the ability of fish populations to recover after a population decline [79]. Hence, the reduction or elimination of fishing mortality following the effective implementation of a MPA is expected to increase population density and biomass as stocks recover from exploitation.…”