Our results show that, although the majority of fishers interviewed (84%) considered that fishing had led to depletion or loss of some species or fishing sites, analysis of their answers reveals a rapid inter-generational shift in their perception of how the seascape looked in the past. The median number of species mentioned by old fishers as depleted was 11, middle-aged mentioned seven and young fishers two (a; Kruskal–Wallis test, χ2=37.65, p<0.001). Since older fishers have had more opportunity to see species loss, we calculated rates of loss by dividing the number of species mentioned by the number of years fishing by each respondent. There was no significant difference in loss rate across generations, indicating no slow down in biodiversity decline (Kruskal–Wallis test, χ2=2.00, p=0.37).
Figure 1 (a) Number of species mentioned by each generation of fishers as depleted (Kruskal–Wallis test, χ22=37.7, p<0.001). Boxes show median, 5, 25, 50 and 95th percentiles of the data; dots show range. (b) Number of sites mentioned by (more ...)
Old fishers remembered times when large and vulnerable animals were much more abundant, as were easily overexploited invertebrates (). These people began fishing when the sea supported abundant medium-sized sharks like the bull shark (Carcharinus leucas), hammerheads (Sphyrna spp.), large groupers (e.g. M. jordani), large snappers (e.g. Lutjanus novemfasciatus), Pacific green turtle (Chelonia mydas agassisii) and large edible invertebrates such as the purple lip rock oyster (Spondylus calcifer) and Cortez conch (Strombus galeatus). They testified how these populations were depleted over the years in which they worked. By contrast middle-aged fishers showed less appreciation of past abundances and few young fishers seemed aware that such species had ever been common ().
The percentages of respondents from three generations of fishers that considered populations of different exploited species to have been depleted by fishing.
Although old fishers recalled an ecosystem in a better condition than that experienced by young fishers, their baselines also appeared shifted from what early Europeans visiting the area witnessed. Few old fishers commented on the once valuable fishery for pearl oysters (Pinctada mazatlanica
; Cariño-Olvera 2000
), abundant and extensive from the beginning of the seventeenth century to 1940 when the pearl banks collapsed (Monteforte & Cariño-Olvera 1992
; Cariño-Olvera 2000
). None of their testimonies fitted with the seascape observed by seventeenth century Spaniards such as Nicolás de Cardona who wrote
along the seacoast of the interior region, over a distance of 100 leagues all that one sees are heaps of pearl oysters
Few also mentioned as depleted the largest predators such as the white shark (Carcharodon carcharias
) and goliath grouper (Epinephelus itajara
), the latter a well documented and common meal of seventeenth and eighteenth century buccaneers who haunted the area (Dampier 1697
Shifting perspectives were also evident across the three generations in the sites mentioned as being depleted by fishing. The median number of sites reported as depleted by old fishers was 4.5, by middle-aged fishers 2 and young fishers 1 (b, Kruskal–Wallis test, χ22=39.0, p<0.001). Again, converting these data to sites depleted by year of fishing experience of respondents, there was no evidence in a slow down of the rate of depletion across generations (Kruskal–Wallis test, χ2=1.2, p=0.54). In total, old fishers named 95 sites as depleted, middle-aged 72 and young fishers 40.
We plotted on maps all sites mentioned as once being productive and now depleted and coded them as coastal, or offshore (seamounts) (c). There was a significant inter-generational shift from the mention of nearshore to offshore sites (Kruskal–Wallis test, χ2=12.0, p=0.002). There was a time when fishers could land large catches and big fish from sites close to shore. As fishing depleted those sites fishers moved further offshore. Amongst younger fishers, many did not realize that nearshore sites had once been more productive, since few mentioned them as depleted. However, they were concerned about more recent impacts of fishing in offshore areas.
Large predators, such as the Gulf grouper, were once common in the area but appeared to exist now only in historical documents and the memories of old fishers. Descriptions by early twentieth century naturalists portray a seascape where Gulf groupers dominated the reef ecosystem (Sáenz-Arroyo et al. in press
). In 1932 the naturalist Griffing Bancroft wrote of Gulf groupers from San Idelfonso Island in the central Gulf of California
In unimaginable numbers, from one edge to the other, Garopuas (sic) haunt the rocky ledges of coast and islands. If a jigger is trolled at a speed of about four miles an hour over the proper bottom there is no question of catching something, the only gamble is in species and size. The slogan ‘a ton an hour’ can often be bettered.2
Richard Crocker of the California Division of Fish and Game concurred, writing in 1937 ‘Sport fishermen who angle in Mexican waters encounter no difficulty in catching their fill of the abundant cabrilla and grouper. In fact they find it virtually impossible to catch anything else along the rocky shores inhabited by these voracious and unwary fish that will strike at any moving object smaller than themselves’.3
Contemporary photographs also picture smiling fishers sporting giant catches (Kira 1999
; ), and many other historical documents agree that this species, which is a rarity today, was once incredibly abundant (Sáenz-Arroyo et al. in press
Figure 2 Photograph of two fishers hauling a good-sized Gulf grouper. Although the photograph is not dated, the harpoon, the canoe and fishers' clothes characterize the middle of last century. Reproduced with kind permission of Gene Kira (Kira 1999).
Only the oldest fishers we interviewed had experienced the heyday of fishing for giant groupers. We asked fishers what had been their best ever day's catch of the Gulf grouper and when they caught it. In the 1940s and 1950s fishers recalled catching up to 25 fish in a day (a
), by the 1960s this had dropped to 10 or 12, and by the 1990s it was one or two. We can also see a shifting baseline in the fraction of fishers from each generation who had ever caught a Gulf grouper. While 96% of old fishers and 90% of middle-aged fishers had caught the species, only 45% of young fishers had. Accepting that younger fishers had had less time to catch the species, it does however provide a context for the finding () that only 10% of young fishers considered the species depleted compared to 56% of middle-aged and 85% of older fishers. We also asked fishers how big the largest Gulf grouper they had landed was and when was it caught. Again, experiences were significantly different across generations (b
). The average size of the largest fish ever caught by old fishers, estimated from a length–weight relationship, was 84
kg, by middle-aged 72
kg and by young fishers 63
kg. This result is not simply an artefact of older fishers being more skilled or having fished for longer. A regression of the year in which fishers recalled landing their largest fish against the size of the fish shows that the biggest fish really are disappearing (c
Figure 3 (a) Size of the best day's catch of Gulf groupers plotted against the year in which the fisher remembered landing it (with a second order regression line shown r2=0.62, p<0.001). (b) Mean weight (+95% CI) of the largest Gulf grouper ever landed (more ...)