24 NOVEMBER 1997. MEXICO: AQUACULTURE

"This is just a short note about the effects of the recent El Nino in our pearl culture operations at Bahia de La Paz, South Baja California. 1. We registered nearly 4 C over the normal maximum temperature we usually read in the Bay, but this was only registered between surface and 4 m depth. This acted to our advantage because we moved the whole installation to deeper waters. The cumulative average mortality was very similar as the normal average we register during the same season and within the same size/age of pearl oysters, this is, very low (2.5 to 3.5 >%).2. On the contrary, we observed an extremely high natural recruitment. Our spat collectors (even the fact that we were not using "the good ones") had averages of 150 spat per unit, when into those kind of collectors we usually had not more than 10 per unit.3. Among the other species associated to collectors of Pinctada mazatlanica (spatfall of this pearl oyster in Bahia de La Paz is in summer), we observed a completely different composition of the one we consider as "standard". Many species were absent and many other were "new". Vertical distribution was also all messed up both on the associated species and in P. mazatlanica. The maximal spatfall of P. mazatlanica takes place between 2 and 6 m depth and it is very rare from 8 m down. This time we got the maximal spatfall between 5 and 12 m depth.4. Every object on the bottom (old tires, ropes, the galvanized pipe structures we use for bottom culture, etc.) was covered with spat of P. mazatlanica. We believe that this event was a very important factor for therecovery of pearl oyster wild beds. We will follow some of these wild juveniles to see how they behave. Maybe in a couple of years the low density ofnatural beds will change positively."--Mario Monteforte <montefor@cibnor.mx>, forwarded by Barry A. Costa-Pierce <bcp@uci.edu>