PRESERVING SPECIES BIODIVERSITY

Having been intimately involved with aquaculture and commercial fishing since 1966, including work on charter sportfishing boats in the Western North Atlantic, culture of finfish in India, Nepal, Philippines, Oklahoma, Maine, and marine algae in Maine, Japan, and Chile, I have observed first hand a most disturbing trend in the quantities, qualities (species), and displacement in the commerical fishery industry and oceans in general. The most serious aspect of what I observe is the massive removal of nutrients that occurs as we harvest the products from the sea, and the slow replacement of these minerals back to the source of origin of the harvest. Since 1991 I have tried to cultivate the Japanese alga 'Porphyra yezoensis' for the production of nori in the west coast of the Gulf of Maine (New Brunswick, Maine) and in every season have lost the crops due to lack of nutrients. These waters are reputed to be some of the most productive in the world. The second trend is the 'fishing down the trophic levels' that has occurred during the past several decades. This has been nicely described by Pauly et al, 1998. They found statistically that there has been an average of about 0.1 drop in trophic level per decade in the species composition of global landings. Both of these factors have a huge impact on species diversity in ecosystems of the seas.

The current global harvest of finfish is approximately 100,000,000 MT and has been static during the 1990s . Fishing pressure has increased as well as becoming more efficient compared to previous decades; what is changing is the composition of the catch. This is definitely not due to changes in the market; indeed governments are increasing their efforts to develop markets for 'under-utilized species' because the 'utilized' are no longer in sufficient abundance. This harvest is equal to roughly 8 million MT of nitrogen being removed from the ocean to the land. Much of this is returned to the sea in the form of sewage near large cities, which are never near the harvest sites. The Mississippi River collects huge quantities of nitrogen and other nutrients from the Midwest of the U.S. agriculture industry and dumps them in the Gulf of Mexico, causing increasing problems with algal blooms but no notable increase in commercial fishery harvests in the Gulf. The time lag which occurs before the nitrogen returns to the fishing grounds is measured in months and years; the primary users of this nutrient, the phytoplankton, have life cycles measured in days and weeks. The others sources of nitrogen- atmospheric transfer (approx..2,500 kg/sq. km/year), rivers and other run-off from land, mineral decomposition in the ocean, and re-cycled nitrogen from remaining organisms from waste and decomposition from mortalities are considerably inadequate to replace the removed nitrogen. This is true with most of the other elements needed to sustain marine ecosystems. The result is an added impact on the change in the species composition of these ecosystems. The demersal species are having a large increase in nutrients resulting in huge biomasses of 10 million MT in just lantern fishes alone (Gjosaeter and Kawaguchi, 1980).

Higher level trophic species have been targeted for harvest generally due to larger size and easier accessibility; as their numbers decline this has at least two major impacts on the ecosystem. The higher predators are no longer there to feed on lower trophic level species, allowing an increase in numbers and biomass of these species, and the removal of nutrients decreases the general productivity of the ecosystem. The Black Sea demonstrates this as 21 of 26 major commercial species are now threatened with extinction, and Ctenophorans have become one of the dominant species of the Sea.

The trend is clear. The solution is simple and difficult. To maintain maximum species diversity in Europe and in all marine ecosystems, simply stop all harvests. With an estimated 100 million workers employed in this harvest globally, this would be difficult. A more realistic approach is to establish large protected areas on commercial fishing grounds to help the populations revive. Two problems occur in this scenario. Poaching has always become a severe problem when protected areas are designated, lessening the impact of the closed area. Allowing substantial harvests also continues to deplete the areas nutrients. The long- term result will be continued depletion of the resources, major changes in the ecosystems resulting in fewer species of little or no commercial importance which over time will have the same affect as a moratorium on all commercial harvests. The only difference is the time.

Aquaculture is not a satisfactory answer. The predominant species cultured at this time are high trophic level feeders (salmon, flatfish, tunas, catfish, shrimp) which require high protein diets. The source of this protein is fishmeal, which accounts for 37% of the global harvest. By harvesting the food for the cultured fish, then harvesting the cultured fish, the net result is the same - displaced nutrients from the ocean. Only if the food for the cultured species were produced by culturing unicellular algae on land would mariculture have a more neutral effect on its environment, assuming its waste products did not accumulate under the grow-out area. In areas where cultivation of macro-algae is extensive (Japan, China), artificial fertilization is increasingly required for successful harvests. The quantity of macro-algae grown, approx. 6 million MT, has not increased, the amount of nutrients have decreased. In areas where shellfish are cultivated, there is a net loss of nutrients as the cultured animals filter feed and remove the phytoplantors and zooplanktors, converting it to shellfish biomass,and we remove the cultured shellfish from the sea.

The best solution for sourcing food for the human population is culturing uni-cellular algae in land-based tanks, such as spirulina, genetically modifying those species that most lend themselves to that practice to produce foodstuffs palatable to us, and probably simulating fish, meat, and poultry tastes. Then there would be no need to produce meat and poultry (the single largest user of fish from the sea is in cattle and poultry feeds) nor any need for harvesting fish for food. The biodiversity of the seas will greatly increase, increasing the opportunities for biotechnological advances in medicines and drugs.

Stephen E. Crawford Aquaculture Consultant, IMR 130 Water ST. Eastport, ME. 04631 207-853-0982; fax 207-853-9570

Lit. Cited:

-J. Gjosaeter and K. Kawaguchi. FAO Fish. Tech. Paper No. 193. 1980.

-Pauly et al. 1998. Fishing down marine food webs. Scinece 279:860-863

-Pauly, Daniel, Villy Christensen, Johanne Dalsgaard, Rainer Froese,

-Francisco Torres Jr. 1998. Fishing down Marine Food Webs. Science 279: 860-863