ENVIRONMENTAL AND SOCIAL IMPACT OF SUSTAINABLE OFFSHORE CAGE CULTURE PRODUCTION IN PUERTO RICAN WATERS
Preliminary results
Water quality analysis
Water samples were taken at the bottom, mid, and surface depths. We also took samples at three depths in a control site (Co) (about 400 m from the cages) to determine if the changes in values are due to the effect of the cages or seasonality. Water samples were taken at north (N), south (S), west (W) and east (E) of each cage, and at 20 and 40 m, and at the center of the cage.
Water analyses indicated no increases in ammonia-N in the bottom samples for the snapper and cobia cages (Fig. 1-2). October and December had similar concentrations of this nutrient at the bottom. Although December shows higher concentration of ammonia-N at mid-and surface waters, they appear due to a seasonality effect because the control site had similar concentrations (Figs. 3-6). It is noted that the concentrations for all months in both cages have been relatively low and normal for this waters (< 3.5 µmol/L).
Nitrite concentrations were low for all the months analyzed (< 3.0 µmol/L) (Figs. 7-12). Nitrite concentrations were higher in August (when there was no nutrient input since the cages were stocked on that date).
Nitrate concentrations were also low for all months analyzed (< 2.5 µmol/L) (Figs. 13-18). Nitrate concentrations were higher in December at the bottom depth and in August at the surface waters apparently due to the seasonality changes because the control site had similar concentrations.
Phosphate concentrations were also low for all months analyzed (< 1.0 µmol/L) (Figs. 19-24). The controls site had similar concentrations suggesting that changes are seasonal.
Dissolved oxygen concentrations during December and January were 88.7% of saturation, with an average concentration of 5.8 mg/L (Fig. 25).
The water temperature declined slightly from December to January (Fig. 26), with an average of 27.4şC. It is noted that the coldest months for Puerto Rican waters usually are December, January, and February (the coldest month).
The chlorophyll-concentrations around the cages during December and January had an average concentration of 10.1 µg/L. It increased slightly during December, but has remained similar from January (Fig. 27).
The water turbidity remained below 20 NTU during December and part of January (Fig. 28). However, the last five days before the Hydro lab recovery, the turbidity increased significantly, reaching 100-120 NTU at January 15-16, apparently associated with the net cleaning process. Please note that Snapperfarm, Inc. cleaned the nets during these days. Thus the increase in turbidity was a temporary situation.
Macroinvertebrate benthic fauna associated with the cages
The total number of micro-benthic organisms near the cages (40 m) during October was almost the double the organisms at the control site. During December, the total number of organisms increased to more than three times the number of organisms found at the control site (Fig. 29-30). These preliminary results suggest that the nutrient input around the cages has resulted in an increase in the macroinvertebrate population. The highest numbers were found near the cobia cages, the cage receiving the most feed. However, initial indications appear that the biodiversity of these organisms has not changed; relative compositions between the snapper and cobia cage are similar (Fig. 31-32).Biofouling in the cage net
This
study examined the fouling organisms on the nets of two offshore fish culture
cages located on the southern coast of
Icthyofauna around the cages
Videos taken before the cages were installed indicated few fish in the water column. Videos taken from June 2002 to January 2003 suggest that there are significant increases in the numbers of fish found near the cages. This study gives a qualitative description of the composition, distribution and relative abundance of fishes associated with offshore-submerged cage systems for the culture of snapper in Puerto Rican waters. Censuses were taken at two submerged cages inIn the data analyzed, the presence of species with juvenile organisms have been high (approximately 26%, 6 species). Many reef fishes use a variety of habitats during ontogeny, often showing distinct spatial separation in settlement areas, nursery areas, juvenile and adult feeding areas (Appeldoorn et al. 1997). All the observed specimens of the genus Acanthurus were juveniles and were mainly distributed in the top of the cage. The fact that there is a considerable aggregation of recruits in an area means that either reproduction or survival is patchy (Hall and Lennert. 1992). In this sense, it is important to note the importance of these cages possibly acting as a nursery structure where juveniles could find the conditions required for existence and survival. The same results have been reported by other studies of floating objects (Deudero et al. 1999). These cages may have important ecological consequences since they act like nursery structures for some species, possibly having an effect on the redistribution of juveniles.
The species that exhibited a solitary behavior were the bigger ones, like Sphyraena barracuda, Echeneis naucrates and Scomberomus cavalla, among others. These species seems to take advantage of their large body size and represent the higher level on the trophic level around the cages.The lack of studies carried out on similar habitats does not allow close comparisons. However comparing with FAD’s studies the richness value obtained here is rather high, taking into account that 22 species belonging to 12 families were found. Since the results reported here correspond only to the fish community associated to the submerged cages between three months, this suggests that the aggregation effect of the cages is really strong to the wild fish community.Weather information
The average tide, air temperature, heat index, dew point, wind speed, and relative humidity are shown in Figs. 32-36. (not yet available on this site)
Miscellaneous
Lobster populations range from 150 to 250 outside of the cages. They appear to be increasing in size. At least one cultured fish had lobster antennae protruding from their mouths. Fishes have been observed eating waste or possibly uneaten feed from the cages.