Spatial distribution of abalone (Haliotis fulgens and H. corrugata) and its time variability; implications for their management.

Abalone fisheries in the central pacific coast of Baja California relies on the exploitation of Haliotisfulgens (green abalone) and H. corrugata (pink abalone). Their catch is regulated under a quotas system annually assessed by the fisheries authority. Because they are sedentary species it is assumed that their density and biomass are roughly constant along the time. Thus, annual biomass assessments are realized only once a year. However, a central question emerges: whether this assumption is true, or density and biomass are changing even in a short time? To respond this question, submarine surveys were carried out at different times, in eight reefs along the same fixed sampling stations. Results showed that both the density and spatial distribution changed just after 24 and 72 h. Similar changes were observed 24 days later. Total abundance changed from 79 specimens at the beginning of the experiment to 46 at the end. In some sites, abundance falls less than 50 %. Changes in spatial distribution wereobserved commonly. The average of the minimum distance within the abalone patches was 0.5 m; however, most patches were only of 2 individuals. We conclude that it is necessary to undertake more than one annual survey assessment to attain average confident figures of density and biomass population, with less uncertainty. Furthermore,assessments should include measurement of size and frequency of the patches, which should be numerous enough to guarantee a successful reproduction, in-order-to maintain the stocks at a sustainable level.