OpinionsEnvironment ConnectionReef fish biomass recovery in marine reserves

Reef fish biomass recovery in marine reserves


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One of the reasons that serve to justify and rationalize the establishment of no-take marine reserves is the potential of these reserves to provide a solution to the loss of biodiversity (including fishery species) and ecosystem structure.

The topic of fish biomass recovery after depleted and degraded coral reefs acquire full protection from fishing is, therefore, of great interest to many scientists as well as fishers.

For the predatory reef fish species belonging to the Families Lethrinidae, Lutjanidae. Serranidae, and Carangidae, the biomass recovery period of time has been estimated at about 15 to 40 years, based on our 17 years of data (Russ and Alcala, 2004).

In the Philippines, the predatory reef fish species mentioned above and other Families, namely Acanthuridae, Scaridae, Labridae, Caesionidae, Siganidae and Haemulidae are considered target or food fishes.

Our underwater visual census of live fish individuals on coral reefs includes estimates of biomasses of species in these Families. Our data used in this presentation were gathered during the period of 26 years (1983-2009) mainly by my colleagues at SUAKCREM (Brian Stockwell, Jasper Maypa, Rene Abesamis) and at James Cook University, Townsville, Australia (Garry Russ).

This paper is an attempt to provide some tentative answers to the commonly asked questions: How long does it take for a depleted reef to recover its historical fish biomass? What is the status of the biomasses of these 10 or so Families on both fished reefs and protected reefs (no-take reserves)?

It is important to state at the outset that the baselines on target coral reef fish variables such as species richness, abundance, and biomass, are not exactly known. The famous fishery scientist, Dr. Daniel Pauly (1995), refers to this situation as the “shifting baseline syndrome of fisheries.”

Despite this lack of baseline, let me suggest an estimate based partly on experience on diving on coral reefs from way from the late 1930s and early 1940s to the 2000s, and partly on estimates in the published literature in the 1940s to 1972.

The seven estimates in the literature from several reefs in the world varied: 10, 45, 50, 60, 100,155 210, all in kilograms/1,000 m2 or tons/km2, depending on which kind of reef was surveyed.

The reef flats had low biomass (10 tons/km2) but the higher profile reefs ranged from 45 to 210 tons/ km2; the mean of these seven published estimates is 90 tons/km2, which may be adopted as the baseline for fish biomass in the 1930s and 1940s.

Those of us who have experience on a reef with a measured fish biomass of 90 tons will recognize that this biomass is characterized by a moderate darkening of the sea bottom when this volume of fish passes at noon of a sunny day.

A biomass of 150 tons at Tubbataha Reef in the Sulu Sea causes a marked darkening of the sea bottom at noontime. A reef with a fish biomass of 100-150 tons is no doubt an excellent reef.

This was the case of most remote coral reefs of the Philippines in the 1930s and the early 1940s. In the late 1940s and the 1950s, Philippine reefs began to slide downhill in terms of fish biomass and live coral cover.

When the concept of no-take marine reserves was first put into practice in the early 1970s, many reefs had already shown signs of overfishing. The fished portion (control sites) of Apo Island reef showed a trend of 20-40 tons/km2. But the adjacent no-take zone (marine reserve) of Apo Island Reef showed an increasing trend from about 15 to 100 tons/km2 during the 14 yearly surveys from 1983-2002, showing without question that protection of the no-take reserve resulted in increased fish biomass to approximate the “virgin” biomass of 100-150 tons/km2.

One can see that the fished portion (85 percent of the total reef area) maintained a low fish biomass simply because it was fished continually. Our independent estimate of the fish removed was at least 15 tons every year from this fished area.

A later published paper showed that about 10 percent of the annual catch came from the reserve (spillover).

In 2002-2009, nine unprotected and fished reefs in the Visayas and elsewhere were surveyed at 14 different times with the underwater visual technique. The results showed biomasses of less than five to ca 40 tons/km2, but mostly at around 5-10 tons/ km2.

I suspect that our findings in the Visayas are also true of other marine areas in the other parts of the country if these areas were surveyed. (Incidentally, our findings are open for any interested person to examine, but I cannot release them because they are not yet published.)

Furthermore, 17 no-take marine reserves (protected) in the Visayas surveyed in 2001 through 2009 showed varying trends in biomass increase: a) one group increased from less than 5 to 150-200 tons/km2 in five to seven years; and b) another group increased from less than 5 to 80-90 tons/km2 in six to seven years.

We do not know yet whether these trends generally hold. But the chances are they would. Continuous monitoring of these reserves, however, is needed.

Summarizing, it appears that most unprotected and fished coral reef areas in the Visayas have lost about 90-95 percent of their fish biomass and only 5-10 percent remain, assuming 100 tons/km2 is the average fish biomass for Philippine coral reefs.

The current baseline for fish biomass in the 2000s must therefore be 5-10 tons/km2. This is a cause for alarm by coastal residents and by the local government units.

In contrast, fully protected (from fishing) coral reefs have always increased their biomass in the course of time during our study.

We must, therefore, counter the finding of low fish biomass in coastal areas by establishing more no-take marine reserves, if we have to sustain the increasing human populations in coastal areas.

As it has been shown that net spillover of adult fish to fished areas occurs when biomasses of reserves are large, it becomes obvious that fishers stand to benefit in terms of increased fish catches from spillover from no-take reserves. There are, therefore, enough good reasons for establishing more no-take marine reserves to be fully protected in order to increase fish catches.

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