Question #3: Can we get more fish or benefits
from fishing while reconciling fishing with
conservation? Keynote speaker: Yingqi Zhou
Q3-1. Food web constraints to getting more fish
and reconciling fisheries with conservation:
Effects of fishing on increasingly smaller
target species, including the effect on life
histories. Food chain effects and fishery
collapse. Session leader: H. Matsuda
11:00a.m. May 4, 2004, Vancouver (Program at a glance)
Hiroyuki Matsuda (Ocean Research Institute, University of Tokyo, Japan)
Ecosystems including fisheries resources are characterized by uncertainty, dynamic properties, complexity and evolutionary response. However, the classical maximum sustainable yield (MSY) theory does not include any of these but assumes (1) perfect information about the stock-recruitment relationship and stock abundance, (2) stable equilibrium, (3) a single stock management and (4) fixed life history irrespective of fishing mortality. The MSY theory and its derivatives have not worked for fisheries management (Hilborn 2002).
FAO (Food and Agriculture Organization of U.N. 2000) noted that about 3/4 of stocks are either fully exploited, overexploited, have been depleted or are recovering from depletion. It should be noted, however, that although the total landings of demersal fishes was saturated by the 1970s, those of pelagic fishes are still increasing, These pelagic fishes fluctuate in stock abundance greatly even without fisheries. When the stock level is at a low level, the impact of fisheries on pelagic fishes prevents the stock from recovering (Kawai et al. 2002). Therefore, in this century, we need to consider how to use nonequilibrial bioresources (Matsuda & Katsukawa 2002, Katsukawa & Matsuda 2003). I propose five principles: (1) do not catch fishes that are at low stock levels; (2) do not catch immature fishes but catch adult fishes; (3) catch fishes that are temporally dominant; (4) in order to achieve these three principles, improve the technology for selective fishing; (5) monitor not only a target species, but its prey and predator and the ecosystem.
Tamura & Ohsumi (1999) estimated that the amount of marine resources consumed by 35 species of cetaceans is 3 to 6 times that taken by human. Competition between fisheries and whales is examined by an ecosystem model (Okamura et al. 2002) but is controversial because indirect effects of the complex marine food web are unknown and indeterminate (Yodzis 2001). This paradoxically suggests that we can get more fish, if it is possible to reconcile fisheries with ecosystems including cetaceans. Whales eat krill, pelagic fishes, lantern fishes and deep-sea fishes and squids, prey abundances which are probably huge and unused by humans. However, we should not repeat overexploitation of deep-sea resources, as we did with terrestrial and coastal bioresources.
Evolutionary responses of resources to fisheries often support counterintuitive policies, e.g., exploitation of smaller fishes (Conover & Munch 2002) and of spawners (Law & Grey 1998). We should take care of scientific meaning of result from studies in evolutionary ecology.
References
Conover DO and Munch SB (2002) Sustaining fisheries yields over evolutionary time scales. Science 297：94-96
FAO Fisheries Department (2000). The state of world fisheries and aquaculture. http://www.fao.org/sof/sofia/
Heino M (1998) Management of evolving fish stocks. Canadian Journal of Fisheries and Aquatic Sciences 55: 1971-1982.
Hilborn R (2002) The dark side of reference points. Bull Mar Sci 70:403-408.
Katsukawa T, Matsuda H (2003) Simulated effects of target switching on yield and sustainability of fish stocks. Fisheries Research 60:515-525
Kawai H, Yatsu A, Watanabe C, Mitani T, Katsukawa T, Matsuda H (2002) Recovery policy for chub mackerel stock using recruitment-per-spawning. Fish. Sci. 68:961-969.
Law R, Grey DR (1989) Evolution of yields from populations with age-specific cropping. Evolutionary Ecology 3: (4) 343-359.
Matsuda H, Katsukawa T (2002) Fisheries Management Based on Ecosystem Dynamics and Feedback Control. Fisheries Oceanography 11: 366-370
Okamura H, Yatsu A, Hiramatsu K (2003) Fisheries management based on ecosystem models. ? A case study using Ecopath and Ecosim ? Fisheries Science 68, 154-157.
Tamura T, Ohsumi S (1999) Estimation of total food consumption by cetaceans in the world’s oceans, Institute for Cetacean Research, Tokyo.
Yodzis P (2001) Must top predators be culled for the sake of fisheries? TREE 16:78-84.