Abundance Of Target Species Research Articles

Relationship between catch, effort, CPUE and local abundance for non-target species, such as billfishes, caught by Indian Ocean longline fisheries

This paper analyses the local relationship between effort, catches, catch per unit effort (CPUE) and abundance of target species (such as tunas) and of non-target species (such as billfishes). The Indian Ocean longline fisheries are taken as an example. This paper evaluates the potential bias in the relationship between local CPUE and abundance when fisheries are increasing their fishing effort. A presentation of the Indian Ocean longline fisheries is carried out. A statistical analysis of CPUE is conducted using a generalized additive model which tends to indicate that the local effort is an important component in the statistical behaviour of the local CPUE. A migratory model in which both resources and fisheries are mobile was built. This model simulates the combined exploitation of two species, a target and a bycatch species, both fished at increasing intensity. This model confirms the potential bias as a result of the concentration of fishing effort in areas of high density of the target species. It also suggests that the CPUE of bycatch species may be more heavily biased because of their status. It is recommended that local fishing efforts should preferably be taken into account in order to calculate the CPUE of both target and non-target species.

Long‐term changes in the trophic level of the Celtic Sea fish community and fish market price distribution

Summary The intensive exploitation of fish communities often leads to substantial reductions in the abundance of target species, with ramifications for the structure and stability of the ecosystem as a whole. We explored changes in the mean trophic level of the Celtic Sea (ICES divisions VII f–j) fish community using commercial landings, survey data and estimates of trophic level derived from the analysis of nitrogen stable isotopes. Our analyses showed that there has been a significant decline in the mean trophic level of survey catches from 1982 to 2000 and a decline in the trophic level of landings from 1946 to 1998. The decline in mean trophic level through time resulted from a reduction in the abundance of large piscivorous fishes and an increase in smaller pelagic species which feed at a lower trophic level. Similar patterns of decline in the trophic level of both catches and landings imply that there have been substantial changes in the underlying structure of the Celtic Sea fish community and not simply a change in fishery preferences. We suggest that the reported changes in trophic structure result from reductions in the spawning stock biomass of traditional target species associated with intensive fishing, together with long‐term climate variability. The relative distribution of fish market prices has changed significantly over the past 22 years, with high trophic level species experiencing greater price rises than lower trophic level species. Although decreased abundance of high trophic level species will ultimately have negative economic consequences, the reduction in mean trophic level of the fish community as a whole may allow the system to sustain higher fishery yields. Management objectives in this fishery will depend on the relative values that society attaches to economic profit and protein production.

Predicting the Potential Future Distribution of Four Tree Species in Ohio Using Current Habitat Availability and Climatic Forcing

We investigated the effect of habitat loss on the ability of trees to shift in distribution across a landscape dominated by agriculture. The potential distribution shifts of four tree species (Diospyros virginiana, Oxydendron arboreum, Pinus virginiana, Quercus falcata var. falcata) whose northern distribution limits fall in the southern third of Ohio were used to assess possible distribution shift scenarios as a result of global warming. Our predictions derive from the results of simulations using (a) forest inventory based estimates of current distribution and abundance of target species; (b) a satellite-based estimate of forest habitat availability; and (c) a tree migration model (SHIFT). The current distribution and abundance of trees was estimated using USDA Forest Service’s Forest Inventory Analysis data and distribution maps from the late 1960s; pre-European settlement forest–nonforest maps were used to represent the fully forested condition for calibration and comparison. Habitat-availability estimates in Ohio were estimated using classified Landsat Thematic Mapper (TM) data from 1994. Tree abundance, forest availability and migration were modeled using a 1-km 2 pixel size. Forest

Ignore fishers’ knowledge and miss the boat

We describe five examples of how, by ignoring fishers’ ecological knowledge (FEK), marine researchers and resource managers may put fishery resources at risk, or unnecessarily compromise the welfare of resource users. Fishers can provide critical information on such things as interannual, seasonal, lunar, diel, tide‐related and habitat‐related differences in behaviour and abundance of target species, and on how these influence fishing strategies. Where long‐term data sets are unavailable, older fishers are also often the only source of information on historical changes in local marine stocks and in marine environmental conditions. FEK can thus help improve management of target stocks and rebuild marine ecosystems. It can play important roles in the siting of marine protected areas and in environmental impact assessment. The fact that studying FEK does not meet criteria for acceptable research advanced by some marine biologists highlights the inadequacy of those criteria.

Detection and quantification of Pseudo‐nitzschia australis in cultured and natural populations using LSU rRNA‐targeted probes

Pseudo‐nitzschia australis Frenguelli is a marine pennate diatom associated with the production of domoic acid— a neuroexcitatory amino acid linked to illness and mortality of humans and wildlife. Distinguishing P. australis from its co‐occurring congeners is labor intensive and time consuming because of a requirement for scanning electron microscopy. Here, we apply large‐subunit ribosomal RNA (LSU rRNA)‐targeted oligonucleotides in whole‐cell and sandwich hybridization formats to identify and enumerate this species collected from pure cultures and natural populations. Whole‐cell hybridization employed fluorescently labeled probes, filter‐based sample processing, and epifluorescence microscopy to enumerate labeled cells. In contrast, sandwich hybridization was accomplished by homogenizing cells in a chaotropic solution and performing two hybridization reactions: capture of LSU rRNA using an oligonucieotide coupled to a macroscopic solid support and binding of signal probe to a region of LSU rRNA near that of the capture site. Sandwich hybrids were detected colorimetrically; color intensity was proportional to the abundance of target species in the original sample. The sandwich hybridization assay was semiautomated with a robotic processor. Both whole‐cell and sandwich hybridization are useful techniques for identifying P. australis as it occurs in nature. Sandwich hybridization potentially offers the most rapid and simple means to accomplish this task when screening large numbers of environmental samples.