Fishing about and about fishing

 

Dr. John F. Caddy is a renowned fishery biologist. In the 1970s and 1980s, we both served at FAO HQ, and I always appreciated his imaginative, unorthodox thinking. He was the man to point out that the continuing growth of fishery yields throughout the Mediterranean could not be supported by its natural primary productivity, but only by the agricultural, municipal and industrial pollution flowing into the Blue Med and carrying huge loads of nutrients. Another point he had made in those days was that fishery management measures as a rule would lag behind what was going on in true time in the sea. It may take a couple of years or more to have catches  sampled and/or surveys performed, the data processed, conclusions drawn and passed on to the management, steps decided on and negotiated with the industry, before they’re finally implemented. When it happens during a shift in the trend of natural stock fluctuation the management measures may prove counter-productive, if catch is curtailed when the stock is already on its way up, or vice-versa, quotas increased while the stock is ebbing.

 

Recently, John Caddy spoke up again. This time, it’s a book he wrote, entitled: “Marine Habitat and Cover - Their Importance for Productive Coastal Fishery Resources” (UNESCO Publishing – www.publishing.unesco.org).

 

What Dr. Caddy is saying, in a nutshell, is that fishery science has been neglecting the effect that modification and degradation of fish habitat and other ecological factors have on fish stocks. Hence, he argues that output-control management is inadequate for restoring depleted fish stocks, and brings up the concept of cover: a complex physical structure that offers its inhabitants a more or less safe refuge from predators. 

 

Fish may need different habitat conditions at different life stages for survival, and habitat malfunction may increase mortality of any stage, from eggs to juveniles thus affecting the whole stock.  In such cases catch control may prove useless. Ecological and management factors must be integrated into a common framework, in which the role of the habitat as provider of protection against predation is of significant importance, especially where it comes to the early life stages of demersal commercial fishes.

 

Caddy believes that the habitat (complex) structure is as least as important for the recovery of depleted resources as the availability of food, and that human activities that have “simplified” coastal habitats have done a lot of damage. He points out to factors, which may contribute to poor recruitment: climate change; overfishing and diseases; changes in species composition; loss of genetic variability; exotic immigrants; juveniles of target species becoming by-catch; pollution, eutrophication (enrichment) and habitat degradation; blockage of migration routes; local extinctions due to habitat problems; destruction of spawning or nursery areas. I would add to this list also the mounting effect of selective fishing that has been creaming off over many generations the larger and more prolific individuals of mainly the longer-living ground fish, which must’ve affected the recruitment, whether or not a genetic change (dwarfism) has occurred in the populations affected. 

 

 

 

 

 

Although Dr. Caddy is paying considerable attention to the inflow of nutrients from land sources, and their effect on fish habitats, I was looking and found hardly any reference to industrial and other types of pollution that contain poisonous and pathogenic, including carcinogenic materials into the marine environment. It goes without saying that some of them, separately, or in a synergy, can affect reproduction and increase mortality at early life stages.

 

 

The more complex is the habitat structure, the more cover it provides to marine organisms. Some very complex sites and areas, such as soft and hard coral reefs, seamounts, rocky sea bed, etc., are very sensitive to bottom-towed gear and land-based sediment runoff, writes Caddy, and their cover quality may become highly affected, while the impact of fishing on fine sediment bottom may be less evident. Bottom gear, however, reduces habitat complexity and affects the composition of the bottom-dwelling community, as for example, reducing the abundance of large mollusks while increasing that of scavengers.

 

It goes without saying that continual trawling modifies the character of the sea bed on trawling grounds. But, this doesn’t necessarily negatively affects groundfish abundance, where fishing effort has been kept within reasonable limits, as can be seen in some areas thus fished for many decades. According to Caddy, however, even where fishing is not excessive, the stock may be affected by loss of cover in that habitat in which this stock spawns and/or grows to size. This would be expressed in poor recruitment (into the fishery) after the survivors, eventually, migrate to the trawling grounds.

Caddy’s book comes timely, in view of the reality in which, in the words of Prof.R.A. Quinones of the Centre for Oceanographic Research in the SE Pacific, who wrote the Foreword… “The limitations to the traditional fisheries management approach based on single stock assessments have become evident…” and … “Alternative approaches …which embrace higher levels of ecological complexity, spatial heterogeneity, climatic influences, and data realities are gaining acceptance in the scientific community”. I hope Prof. Quinones is not over-optimistic, but Dr. Caddy’s contribution no doubt should enhance this acceptance. Those “alternative approaches” should’ve been long ago embraced by the established fishery science and management, but they were not. Anyway, not yet, but sooner or later they will.

Dr. Caddy is discussing also remedies to the deterioration of complex habitats, such as setting up of marine protected areas (MPAs), especially over sensitive habitats, setting up of artificial reefs, (preferably within MPAs), vertical structures, restoration of habitats and more. 

Unfortunately, I’m unable to give here a full justice to this book. The best I can do is to recommend it to all studying or involved in fishery sciences and management, and marine ecology. This includes fishermen and industry representatives whom Caddy’s texts would help to appraise whether habitat and other factors are taken into account in scientific assessments and the respective management decisions aimed at their fisheries.