Density estimates of giant red sea cucumber (Parastichopus californicus) populations by dive survey, in the Gulf Islands and Jervis Inlet areas, British Columbia, Canada, in November 1997 and January 1998

Dive surveys of sea cucumber (Parastichopus californicus) populations were conducted in the fall of 1997 in the Gulf Islands, and during the winter of 1998 in Jervis Inlet, BC, Canada. The Gulf Islands survey was a joint effort between the Department of Fisheries and Oceans (DFO), the Sea Cucumbers Harvesters Association of BC (PSCHA), and the Cowichan Band. The Jervis Inlet survey was completed without First Nations involvement by PSCHA and contracted third party participants. Each survey area constituted approximately 400 km of shoreline. Field methods consisted of counting the number of sea cucumbers in 4-metre wide strip transects, randomly placed within six randomly selected sites in each area. In addition, three smaller sites, measuring 200 m wide each, were intensively surveyed with random and systematic transects, followed by a complete harvest to obtain the true population size. Transect sampling in the Gulf Island survey produced a mean density estimate of 3.10 +/- 1.15 SE sea cucumbers per meter of shoreline while densities of 9.53 +/- 1.28 were found in the Jervis Inlet survey. Most sea cucumbers were found between 12 and 18 m in the Gulf survey and between 4.5 and 9 m depth (chart datum) for Jervis Inlet. The greatest density in the Gulf Islands survey was found on boulder and cobble substrate, while mixed soft and hard substrate produced the greatest density in Jarvis Inlet. For most of the intensive sites, estimates of the actual population size was within 90% of the confidence limits of the mean obtained from random transects. In the medium and low density sites of the Jervis Inlet, however, the population size was under estimated by transect sampling. Eight transects in one site in Jervis Inlet were surveyed twice. Half of these pairs had similar densities while the other half had densities that differed by a factor of as much as 14. The individual site means, however, were not significantly different.