Habitat degradation and fishing effects on the size structure of coral reef fish communities

Abstract

Overfishing and habitat degradation through climate change pose the greatest threats to sustainability of marine resources on coral reefs. We examined how changes in fishing pressure and benthic habitat composition influenced the size spectra of island-scale reef fish communities in Lau, Fiji. Between 2000 and 2006 fishing pressure declined in the Lau Islands due to declining human populations and reduced demand for fresh fish. At the same time, coral cover declined and fine-scale architectural complexity eroded due to coral bleaching and outbreaks of crown-of-thorns starfish, Acanthaster planci. We examined the size distribution of reef fish communities using size spectra analysis, the linearized relationship between abundance and body size class. Spatial variation in fishing pressure accounted for 31% of the variation in the slope of the size spectra in 2000, higher fishing pressure being associated with a steeper slope, which is indicative of fewer large-bodied fish and/or more small-bodied fish. Conversely, in 2006 spatial variation in habitat explained 53% of the variation in the size spectra slopes, and the relationship with fishing pressure was much weaker (approximately 12% of variation) than in 2000. Reduced cover of corals and lower structural complexity was associated with less steep size spectra slopes, primarily due to reduced abundance of fish < 20 cm. Habitat degradation will compound effects of fishing on coral reefs as increased fishing reduces large-bodied target species, while habitat loss results in fewer small-bodied juveniles and prey that replenish stocks and provide dietary resources for predatory target species. Effective management of reef resources therefore depends on both reducing fishing pressure and maintaining processes that encourage rapid recovery of coral habitat.

Factors affecting the fishing impact on cartilaginous fishes in southeastern Spain (western Mediterranean Sea)

“…Lunar rhythms in commercial fisheries have also been widely reported (e.g. Moore 1958, Wilson et al 2010. Commercial trawl fishermen in northeastern New Zealand believe that at certain phases of the moon fish are more abundant, or at least more easily caught (McDowall 1969), and personal communication from local fishermen confirmed this close relationship between the abundance of the catch of different species and the phase of the moon.…”

Complex reef architecture supports more small-bodied fishes and longer food chains on Caribbean reefs

“…The size-frequency distribution (size spectrum) of fish captures the size distribution of energy in the ecosystem and describes the flow and depreciation of energy toward larger individuals and species. The size spectrum represents, in effect, the total amount of energy in the ecosystem with the intercept reflecting the overall productivity or energy entering the community (Jennings 2005, Wilson et al 2010) and the slope representing the flow and depreciation of energy across fish size classes (Boudreau and Dickie 1992, Kerr and Dickie 2001, Jennings 2005. The size spectrum of the fish community on each reef was calculated by summing the total number of individuals in each of the five 10 cm length categories, up to 50 cm.…”

Evaluating local rules and practices for avoiding tragedies in small-scale fisheries of oxbow lakes, Southern Bangladesh

“…In many cases, the rules related to the suspension of fishing are scientific, as fishing has a direct impact on habitat features such as the disturbance of natural food webs (e.g. the destruction of bottom features and the uprooting of aquatic plants) as confirmed by other research works on ecology (see Turner et al 2001;Wilson et al 2010). The fishers of the Porakhali site informed me that habitat disturbance leads to less availability of foods and that multiple hauling in closed environments such as the oxbow lakes ultimately causes weight loss in the available fish.…”

“…In contrast, interim moratoriums are implemented several times in a fishing season to keep fish healthy from the effect of recurrent gear operations. Fishing practices related to habitat destruction are well documented in many studies across the globe and it is confirmed that recurrent hauling affect fish health and related ecosystem properties such as destruction of bottoms and aquatic vegetation (Hall 1999;Turner et al 2001;Wilson et al 2010). Although fishers are not blessed with access to scientific information on fishing-related damages, and although support from state department (e.g.…”