Pablo is travelling to Australia for three weeks to meet with Dr Jeremy Prince, the scientist behind The Barefoot Ecology Toolbox. Pablo wants to learn how to emulate this toolbox’s success when incorporating fishermen’s knowledge into fisheries management plans. You can read all of his blog posts here.
It’s a Wonderful Life
I just can’t help it. Every year they show Frank Capra’s classic It’s a wonderful life! And I’m always touched. George Bailey is about to commit suicide from a bridge when he sees an old man nearly drowned and is forced to rescue him. Clarence, the old man, is actually his guardian angel. “I wish I had not been born” says George at one point and Clarence makes this true. When George returns to his village no one recognizes him and everything is different. Actually, everything is much worse. All the good deeds that George did for his family and neighbours during his entire life never were performed. The result is catastrophic for the town. Desperate, George returns to the bridge and begs for his lost life. When his wish is granted, George runs through the village greeting his old neighbours, which now recognize to him “Merry Christmas!” he yells.
Bloody hell! I’m in tears again.
Stephen Jay Gould used this same argument in his book Wonderful Life (1989) to illustrate the importance of chance in the history of life. Gould argues that the evolutionary engine is mainly conditioned by contingency, not causation. Beyond Gould, some historians today believe that the counterfactual history (speculation about what would have happened if something would never happened), constitutes a valid method for the study of history.
Jeremy Prince and the abalones
An abalone in the South of Australia
© Pablo Pita Orduna
In this sense, one might wonder what would have happened if Jeremy Prince would have never become an abalone diver. Jeremy developed a visual method for evaluating abalone stocks based on the proportion of animals in the reproductive stage. Terry Adams, an experienced diver gave him a clue. “Sometimes, we fish all the abalone in a reef. We left not a single animal. When we return after a while, they are back again” Terry confided him once “Where do they come from, Jeremy?” Both Terry and Jeremy knew that the abalone grow and move slowly, so that colonization processes from nearby reefs is very slow. “You can do it for some time” Terry went on “You fish them all and they come back, until suddenly one day they are gone, never to return.”
Terry also told him that they occasionally fish strangely flat and clean abalone, with no algae on its surface. Jeremy realized that they were immature abalone. Their shells are less bulky than those of adults because of their smaller body mass. Jeremy also found that those young abalones are hard to see because they hide in crevices under rocks. So their shells have no algae, as they do not get light enough.
“That’s it!” Jeremy inferred. When divers fish all abalone in a reef, they leave the immature, hidden under the rocks. So, after a time, they mature and colonize the surface. When divers return, apparently all is quite well again. In addition, there are some generations of juveniles in a sort of maturing queue, so that the process can be repeated several times, until they simply go extinct.
Problems assessing population sizes
Jeremy has been successfully using a visual evaluation method for some years, as it is very fast and cheap, but it has always been aware of its limitations: it is inaccurate and overly conservative. The more accurate a fisheries assessment, the higher risks can be assumed by managers, and therefore, fishermen can obtain higher catches. But the best evaluations are prohibitively expensive. It is very difficult to estimate the amount of spawning in a population, especially for populations with a long history of exploitation. Years are needed and a lot of specialists with a high level of scientific knowledge to know the age structure, growth, egg production, natural and fishing mortality, biomass and recruitment of a fish population.
Fortunately for this story, in addition to being an abalone fisherman, Jeremy is an experienced fisheries biologist. Thus, he was aware of that fishing alters the size structure of exploited populations. He also knew that the amount of spawning in a population can be measured in relative terms, as the Spawning Potential Ratio or Spawning per Recruit (SPR). This can be applied both to the average individual in a population, as for a population in balance with a steady fishing effort. The SPR is inversely proportional to the intensity of fishing, so a 50% SPR will allow a recovery of the resource and <20% SPR will jeopardize the future of the fishery.
Eureka!
Adrian Hordyk © Pablo Pita Orduna
Jeremy questioned himself for many years about the relationship between the SPR and the abalone shapes. “The height to length ratio of the shell, is not a 2-dimensional index of change in volume? And is not volume an index of weight?” He asked himself while being walked by his dog to the beach. And suddenly something clicked in his brain “Then the SPR can be estimated in the abalone as a direct function of the weight!” He exclaimed in high voice, so people nearby were startled and walked away, casting suspicious glances at him. But, if this was true for abalones, what about other species?
Too much work waiting! And three kids! The idea was shelved in a drawer for long and it was in real danger of being forgotten forever. Until chance, in the form of Adrian Hordyk, a doctoral student rescued it from oblivion. Or maybe Adrian was predestined to meet Jeremy. They analyzed the relationship between SPR, growth and size for a wide range of marine species, from snails to whales. Eureka! There is a simple and generic relationship between SPR and body size.
Developing the toolbox
Jeremy and Adrian are nearly finishing a tool to estimate the current SPR by using the size of maturity of the species and some information about the body size of the population. A tool that can perform a stock assessment with a simple spreadsheet and data from the fishery itself! This tool can be a revolution for the management of fisheries, particularly for small scale fisheries, traditionally poor in data and funds for their management.
We will try to apply the tool to evaluate razor clam fisheries in Galicia. Thus, the Galician razor clam divers are indebted to abalone divers from Australia. Similarly, I am indebted to Jeremy and Adrian for their excellent reception in Australia. Maybe one day we can return the favor. In any case, I believe it was lucky for the Galician razor clams that Jeremy decided one day become an abalone fisherman.
Abalones at different stages of maturation.
The immature abalone (left) and the mature animals (right; © Jeremy Prince)
