Estimating the abundance of clustered and cryptic marine macro-invertebrates in the Galápagos with particular reference to sea cucumbers
Shepherd, Scoresby. A. | Toral-Granda, Veronica | Edgar, G.J.
Estimating the abundance of marine macro-invertebratesis complicated by a variety of factors: 1) humanfactors, such as diver efficiency and diver error; and 2)biological factors, such as aggregation of organisms,crypsis, and nocturnal emergence behavior. Diver efficiencyvaried according to the detectability of an organismcausing under-estimation of density by up to 50% in somespecies. All common species were aggregated at scalesfrom 10-50 m. Transects need to be long enough to transcendthe scale of patchiness to improve accuracy. Somespecies of sea urchins and sea cucumbers (pepinos) whichare cryptic by day emerged at night so that daytimecensuses underestimated their abundance by up to 10times. In the sea cucumber fishery, estimates of abundanceneed to be made at the scale of the population, i.e. athundreds of km. A strategy for this is proposed.
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