UC San Diego Library – Scripps Digital Collection

This bulletin is one of three large publications summarizing kelp investigations at the University of California's Institute of Marine Resources. The general objective of the bulletin is to assess the impact of man's past, present, and future activities on the kelp-bed environment. Possibilities for future improvement are examined in the opening chapters which describe the life history of the giant-kelp plant and show how this knowledge can be used for culturing and transplanting. Ecology of kelp-bed fishes is treated in detail as a background for evaluating influences of human activities. The distributions and ranges of physical parameters important to fishes are outlined with emphasis on temperature, wave action, visibility, and topography. Diets, behavior, preferred habitats, abundances, and life histories of kelp fishes are described, showing the ecological roles played by kelp as a food source, shelter, attractant, and vehicle for making phytoplankton productivity more available to associated fauna. It was found, however, that kelp was not a habitat requirement for most fishes, nor did it increase species diversity significantly. There was evidence that it may contribute to greater standing crops of fishes but bottom topography was considered a more important attractant. It was estimated that kelp harvesting removed an annual maximum of about 10 percent of the food supplies available for fishes. This was not considered serious because generally there appear to be ample food reserves in kelp beds.

Statistical correlations were sought between harvest returns and sportfish catches and catches per unit of effort. Neither statewide totals nor selected situations representing southern, northern, and island environments yielded any relation. Analyses were broken down to the more important groups or species of sportfishes and the only relation observed was a negative correlation between California barracuda catches and harvest yields. Since barracuda are pelagic the relation was considered to be indirect, resulting from interactions with ocean temperature. Fishing was better in beds harvested more frequently. Fishing in deteriorating beds was analyzed. Generally emphasis shifted to new groups of sportfish when more conventional fisheries declined. Statistical treatment was extended to comparisons of adjacent kelp beds that had been subjected to quite different intensities of harvesting. Harvest yield was not affected by harvesting intensity for the 11-year period examined.

Kelp was sampled as it came aboard a harvesting vessel and about one third of the motile canopy fauna was removed from the habitat. The attached fauna, however, was entirely removed. Physiological studies indicated that cutting did not influence photosynthesis in adjacent kelp tissues of the cut frond. Growth of young fronds was, in some cases, retarded for periods up to a month but in other cases growth was stimulated. The complex interplay of environmental variables probably determined the character of any changes in growth rate. The interplay was described by a mathematical model and five cutting experiments were undertaken to test model predictions. Results were considered satisfactory.

It was generally concluded that giant kelp encourages development of a rich associated fauna. No adverse influence of harvesting could be found among the statistics or field observations for the periods studied. The need for intelligent management is stressed to ensure that optimum utilization of the kelp resources will continue.