Definitions and History of Stocking Cultured Organisms into the Sea

Marine Fisheries Enhancement Background

Hatchery-based fisheries enhancement lies at the nexus between sustainable fisheries management and fish and shellfish culture. 

Definitions: There are three basic types of fisheries enhancement (source: Bell et al., 2008)

  1. Restockingthe release of cultured juveniles into wild population(s) to restore severely depleted spawning biomass to a level where it can once again provide regular, substantial yields. This may involve re-establishment of a species where it is locally extinct to rebuild a fishery, or for conservations purposes (i.e. conservation hatcheries).
  2. Stock Enhancementthe release of cultured juveniles into wild population(s) to augment the natural supply of juveniles and optimize harvests by overcoming recruitment limitation.
  3. Sea Ranchingthe release of cultured juveniles into unenclosed marine and estuarine environments for harvest at a larger size in ‘put, grow, and take’ operations. Note that the released animals are not expected to contribute to spawning biomass, although this can occur when harvest size exceeds size at first maturity or when not all the released animals are harvested.

Although the goals of any given stocking program vary, typically they seek to:

  • provide additional catch for commercial and recreational fishermen
  • rebuild spawning stock biomass for the promotion or acceleration of recovery
  • ensure the survival of stocks threatened by extinction
  • mitigate losses due to anthropogenic effects.

Marine Fisheries Enhancement History: (see Footnotes for additional background)

Stocking cultured organisms is not a new strategy for replenishing depleted marine fish stocks in the US.  The first marine stock enhancement programs in the United States started in the late nineteenth century, and coastal hatcheries were built and operated successfully in Gloucester and Woods Hole, in Massachusetts, and Boothbay Harbor in Maine.  For over sixty years many millions of young cod, haddock, pollock, winter flounder, and even lobster were released annually in an effort to augment wild populations.  Apart from the latter, the programs for marine fish were subsequently discontinued and the hatcheries closed.  Primarily, this was because there was no way to evaluate whether releases of juveniles caused measurable increases in the landings of adults.  This was hardly surprising.  At that time there were no effective methods for marking hatchery fish and so there was no way to monitor survival and growth and no way to determine if stocking actually contributed to rebuilding the population. Furthermore, there was little scientific knowledge of the early life histories of these fish in nature, thus the appropriateness of the receiving environment chosen for releases was largely unknown.  Aquaculture techniques for marine fish that spawn in seawater were undeveloped; eggs and yolk-sac fry could be released, but the technology for mass production of fingerlings didn't begin to appear in Europe and North America until the 1970's.

Greater scientific recognition of the challenges, together with significant advances in marine fish breeding and propagation technologies, have given a renewed interest in stock enhancement to replenish declining fish and shellfish stocks.  But will today's fisheries scientists succeed where the early pioneers failed? Clearly, there is high potential to replenish depleted stocks; first, avances in aquaculture technologies now enable large numbers of high-quality disease-free juveniles to be produced in hatcheries, and there is a far greater understanding of the ecological requirements of the receiving waters.  Second, there is a wide array of high-tech marking techniques available and more sophisticated methods to measure growth and survival and monitor contribution to the fishery.  Third, many new projects are addressing critical uncertainties about stocking (see Coleman et al., 1998; Howell et al., 1999; Leber et al., 2004; Bell et al., 2005, 2008; Lorenzen, 2008; Zohar et al., 2008). Marine stock enhancement programs are well underway overseas, and early results have been promising, particularly in Japan (Masuda and Tsukamoto, 1998; Hilborn, 1998) (see Footnotes for references and additional articles).

In the 1990's marine stock enhancement began to move beyond the early fact finding stage that Kuhn (1970) observes characterizes new fields of science. After a century of preoccupation with fish culture, investigators of marine enhancement (i.e. focused on marine spawners) began to publish tests of the hypothesis that cultured marine fish could survive in the wild and contribute to fishery landings. A rapid expansion of scientific studies and philosophical debate regarding stocking has begun, following initial publications by researchers in Japan and Norway (Tsukamoto et al. 1989; Kristiansen and Svåsand, 1990; Svåsand and Kristiansen, 1990a,b; Svåsand et al., 1990), and earlier work with salmonids in the USA and Canada (e.g., Hager & Nobel, 1976; Bilton et al., 1982) (e.g. see studies and additional citations in Munro and Bell, 1997, and in symposia proceedings edited by Lockwood, 1991; Danielssen et al., 1994; Schramm & Piper, 1995; Coleman & Travis, 1998; and Howell, Moksness and Svåsand, 1999; Leber et al, 2004; Bell et al., 2005, 2008).  Marine stock enhancement has begun to be treated scientifically (see discussions in Cowx, 1994; Blankenship and Leber, 1995; Munro and Bell, 1997; Leber, 1999, 2002, 2005; Leber et al., 2004; Bartley and Leber, 2004; Bell et al., 2005, 2006, 2008; Lorenzen, 2005, 2006, 2008; Zohar et al., 2008, and others) (see Footnotes).

Now, we must deal with the lack of theoretical development in marine stock enhancement and the clear need to reduce uncertainty about the effects of hatchery releases in coastal environments. Wider use of the scientific method and “strong inference” (Platt, 1964) would advance knowledge in this branch of fisheries science considerably faster than its current pace (Leber, 1999). We can characterize much of the experimental work now emerging in this field as a period of trial-and-error evaluation of the hatchery-release hypothesis (releasing cultured fish can increase fishery production).  We have entered a passive-adaptive assessment phase of marine stock enhancement, which is best described by Walters and Hilborn’s (1978) (and see Hilborn and Walters, 1992) passive-adaptive management approach. Platt (1964) argues that, for exploring the unknown, there is no faster method than “strong inference” — the systematic application of the age-old scientific method of inductive inference that dates back to Francis Bacon. What makes “strong inference” so effective is systematically “...recycling the procedure, making sub-hypotheses or sequential hypotheses to refine the possibilities that remain; and so on” (Platt, 1964). A key component of “strong inference” is acknowledging the competing alternative hypotheses (major uncertainties) that could explain an observation, and then rigorously weeding out the false alternatives through experimentation. Platt reminds us that for a hypothesis to be testable we must be able to state what conditions would show the hypothesis is false (Popper, 1959, 1965). Walters and Hilborn (1978) reiterate Platt’s argument about exploring the unknown, but add a caveat for fishery management, “We learn most rapidly by introducing large disturbances and much monitoring, but we incur high risks and costs by doing so”  — the “dual control problem.”

The paradox is that to advance this field we must experiment; yet funding for marine stock enhancement research lies largely within the management agencies that are implementing hatchery releases. By mandate, the agencies must manage resources (i.e. implement enhancement, not study it). The solution to this paradox is to gear up long overdue research programs to evaluate the range of critical uncertainties that cloud our understanding of stock-enhancement potential, and to engage resource management in active-adaptive management (Hilborn and Walters, 1992). With this approach, risks of failure are restricted to substocks of the stocks being managed, allowing systematic experimental evaluation of critical uncertainties to become an integral part of fisheries management strategy.  Active-adaptive management is essentially “strong inference” adapted to fishery science. A quick scan of Platt’s (1964) paper reminds us also that it is the systematic application of a logical tree of hypothesis tests and exclusions that produces much more rapid progress than in fields of science that use other approaches.  Coupling “strong inference” and active-adaptive management principles to marine stock enhancement research is the logical next phase of this field.
The new pioneers in marine enhancement are fisheries scientists and fishermen, working together on a shared but carefully allocated resource, as exemplified in Japan.  The Japanese program involves about 80 species of marine fish, mollusks, and crustaceans.  The principal enhanced marine fisheries are yesso scallop, Kuruma prawn, red sea bream, and flounders. The practice benefits from the country's extensive continental shelf but it is estimated that stocking accounts for 90% of the chum salmon fishery, 50% of the Kuruma prawn catch, up to 75% of red sea bream, almost all the scallop harvest, and up to 40% of the flounders (Kitada et al., 1992).  Techniques used by the Japanese to support hatchery releases include habitat restoration, predator removal, and behavioral conditioning.  There is also a strong commitment to the program by coastal fishing communities.

Another pioneering country is Iran, which, since the break up of the USSR, now shares the fisheries resources of the Caspian Sea with four other states.  Within its zone, fisheries scientists in Iran raise and release about 12 million juveniles of indigenous sturgeon species, which support almost the entire nationally-controlled fishery and therefore the valuable caviar industry.  In addition, state hatcheries release juvenile bream, kutum, pike-perch, and Caspian trout, all of which support fisheries harvested by licensed coastal cooperatives (Bartley and Leber, 2004).

Other countries active in marine stock enhancement include Australia, China, Denmark, France, Iceland, Korea, Norway, Spain, Thailand, U.K., U.S.A., and many Island nations of Oceania have active programs for restocking their indigenous populations of mollusks, such as giant clams, pearl oysters, trochus, and green snails.

There are a few marine stock enhancement programs in the U.S., and several research and development projects are underway (see summary of these in Leber, 2004; and see links to US projects).  In addition to the well-established program for lobsters in Massachusetts, there are pioneering projects for blue crab (Maryland, Virginia, North Carolina and Mississippi), king crab (Alaska), lobster (Maine), red drum (Florida, South Carolina and Texas), Pacific threadfin, mullet, and snapper (Hawaii), red snapper (Mississippi, Alabama and Florida), white seabass (California), summer flounder (North Carolina), cod (Maine), lingcod (Washington), snook (Florida), winter flounder (New Hampshire) and various mollusks (several states along all three US coasts). The largest of the marine stock-enhancement programs in the U.S. is the red drum program in the Western Gulf of Mexico (Texas), where Texas Parks and Wildlife (TPW) annually stocks ~ 30+ million hatchery reared early juveniles (25 - 30 mm in length, McEachron et al., 1998). Texas also stocks spotted seatrout.

Although strides are now being made in gaining a scientific understanding of the stock-replenishment potential afforded by hatchery releases, many unresolved questions remain.  SCORE scientists are conducting key experiments to unravel critical uncertainties about how to ensure biological, ecological, and economic effectiveness in stocking programs. Only through a rigorous research-and-development effort will we understand how and whether stocking hatchery-reared organisms can be used successfully as a fishery management tool.

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