Shark Conservation in the Western North Atlantic: A Perspective

By George H. Burgess

Sharks have been sought by fishers for thousands of years. Early fishers caught sharks on wooden or bone hooks, ate the meat, and used the teeth for tools and weapons. Sharks were commercially fished on both coasts of the United States in the 1930's and 1940's. Livers, with their high vitamin A content, and shark skin, utilized in making leather, were the most valuable portions of the shark. These fisheries disappeared after Vitamin A was synthesized in the late 1940's. Current interest in sharks has focused on the meat, which has only recently received acceptance on dinner tables in the United States, and especially the fins, exported to the Orient. Shark fins are made into shark fin soup, considered a delicacy in the Far East. The fins are selling for $25 or more per pound off the boat, making them more valuable than any other U.S. seafood product. Other sharks are caught and discarded as by-catches of other fisheries and by sport fishermen. Sharks are relatively easy to capture using hook and line, gill nets, and long lines; 14% of the commercial catch is made using gill nets, 80% using longlines.

Sharks are extremely vulnerable to overfishing, lacking the ability to withstand long-term, sustained fishing pressure. Historically, major shark fisheries throughout the world have exhibited similar patterns of development and failure. Well-documented declines following spectacular rises in catches have proven to be the norm in shark fisheries. Historical shark fishery crashes include the California soupfin shark in the1940's; the Australia schoolfin shark in the1940's, 1950's, and 1970's; the porbeagle shark in the 1960's; and the basking shark in the 1950-60's. The U.S. east coast shark fishery is currently undergoing a similar decline.

WHY ARE SHARKS VULNERABLE TO OVERFISHING?

Under ordinary circumstances, that is, when dealing with fishes other than sharks - the bony fishes, overfishing is of less concern since populations of most of these commercially harvested species are better able to withstand the assault of prolonged human fishing. Sharks, however, have several biological characteristics that differ from those of most foodfishes. These aspects of their life histories have served sharks admirably for millions of years in their roles as apex predators, but now they have become serious liabilities when faced with the unnaturally high predation pressure of human fishing. Sharks: 1) are slow growing and long-lived,

2) are slow to reach sexual maturity,

3) have a long reproductive cycle,

4) produce low numbers of young,

5) often have specific mating and nursery areas, and

6) are highly migratory.

GROWTH AND AGE OF MATURITY

One of the major problems faced by fishery managers is a paucity of good age and growth studies. Many species of sport or commercial importance have not been studied, or have not had their ages "validated" (verified by independent means such as tetracycline marking or marginal increment analysis). In species studied, some commonly live to 15-30 years of age, and there are species that probably live to 50 years of age or longer. Growth is often slow: dusky (Carcharhinus obscurus) and sandbar sharks (Carcharhinus plumbeus) grow at 10 cm/year while young and 5 cm/year as subadults and adults; tiger sharks (Galeocerdo cuvier) grow quickly at first (25-30 cm/year), then slow down to 5-10 cm/year as subadults and adults. Blacktip sharks (Carcharhinus limbatus) also grow quickly initially, then grow at about 5 cm/year as adults.

Most of the shark species contributing to commercial and sport catches reach sexual maturity at an advance age. The dusky shark matures at 17 years of age and the sandbar at 15-16. The spiny dogfish (Squalus acanthias) must wait 10-13 years to reach maturity. Lemon (Negaprion brevirostris) and bull (Carcharhinus leucas) sharks also mature at advanced ages. Blacktip and Atlantic sharpnose (Rhizoprionodon terraenovae) sharks are among the quickest to reach maturity at 4-7 and 3-4 years of age, respectively. Tiger sharks mature at an intermediate 8-10 years of age.

REPRODUCTION

Sharks reproduced via internal fertilization with males using modified pelvic fin elements called claspers. There are three types of reproductive strategies commonly employed in this group:

Oviparity. This is the most primitive mode of reproduction. Females have large eggs with yolk to nourish the young through development. There is no parental care invested in development of the young. An egg case made of protein fibers covers the developing embryo and is released to the environment. Development continues in the egg case for several months to a year. Examples of oviparous are the cat (Scyliorhinidae) and Port Jackson or horned (Heterodontidae) sharks.

Ovoviviparity. This the most common mode of shark reproduction. Embryos in the female's uterus are nourished by yolk stored in a yolk sac. There is no placental connection to the mother. Young are born after development is completed. Among the interesting variations in ovoviviparity is fetal cannibalism. In sand tiger sharks (Odontaspididae), first embryo to use up yolk eats the remaining embryos, then consumes unfertilized ova; thus, one young is born from each uterus, or two in total. Stewart Springer, one of the greatest students of sharks in this century, discovered that the sand tiger shark (Odontaspis taurus) had this type of development when he was bit by a full-term pup while probing the uterus of a pregnant female with his finger! Oophagy, in which young eat non-fertilized ova after using up their own yolk early in development, is also found in other lamnoid sharks, the makos and their kin. The ovoviviparous nurse shark (Ginglymostomidae) produces odd internal egg cases. Other examples of ovoviviparous sharks are the spiny dogfishes (Squalidae), six- and seven-gill sharks (Hexanchidae, Heptranchidae), and angel sharks (Squatinidae).

Viviparity. This is the most advanced mode of reproduction and is the type employed by most commercially important species. Embryos initially grow using stored yolk. Later a pseudo-placental connection is formed between the yolk sac and the uterine wall. Resulting embryos usually reach a quite large size at birth. The requiem (Carcharhinidae) and hammerhead (Sphyrnidae) sharks are the chief viviparous groups.

REPRODUCTIVE RATE

Most sharks have independent gestation periods and ovarian cycles, that is, they do not begin egg development until after giving birth. Thus, including gestation, they give birth about every two years. Most major sport and commercial "target" species follow this plan. Other species, such as hammerheads and sharpnose sharks, concurrently gestate and develop eggs, thus they can mate immediately after giving birth, producing yearly litters. The commercially-important spiny dogfish gestation period is 18-24 months, the longest of any vertebrate. It concurrently develops eggs, so it produces litters every two years. Typical litter sizes are ten or less; for example, the blacktip produces only 4-8 young, the Atlantic sharpnose 4-6, and the sandbar shark about 10. The tiger shark is atypical in having about 30-40 per litter (occasionally more than 50).

MATING AND NURSERY AREAS

Most sharks have specific mating areas. If these can be identified by fishers, they easily can be severely overfished during mating season. Nursery areas are located in inshore shallows or estuaries for most commercial species. Nursery areas offer young sharks abundant supplies of food and some protection from their major natural predators, larger sharks. Larger individuals of many shark species are found predominantly in deeper offshore waters, leaving shallower depths to the young. Many inshore nursery areas are threatened by human development, pollution, and commercial and sport fishing. These areas are fished extensively by inshore longliners and especially by shrimp trawlers, where sharks largely become part of discarded bycatch. Nurseries also are prime angling areas for sportsfishers. Inshore nurseries are not covered by the federal management plan, so they must be regulated state-by-state. Florida and Texas are two states that have actively protected inshore nursery areas through regulations; others, such as North Carolina, have important nursery areas that should be regulated. Florida regulations should serve as a model for other states, limiting catches to one shark per person per day and two sharks per boat and prohibitting "finning," the inhumane and wasteful practice of removing fins after capture without retaining the carcass for consumption.

MIGRATIONS

Most species of sharks in the western North Atlantic are highly migratory, following discrete seasonal routes. Most of the larger species involved in fisheries move northward along the U.S. east coast as water temperatures increase in the spring and summer and move southward in the fall as temperatures drop. In addition, there are inshore-offshore movements tied to water temperature and reproduction. Because these movements are reasonably predictable, knowledgeable fishers are able to "follow the pack" during the migratory process, and can target certain species and even certain sizes.

TO SUMMARIZE

1) sexual maturity is not reached until 8-20 years of age in most sport and commercially important carcharhinid species and the spiny dogfish,

2) most harvested species produce a litter of young every two years,

3) usually there are 10 or fewer young per litter,

4) species specific mating and nursery areas are threatened, and

5) migratory routes and timing are reasonably predictable events that foster an effective targeted fishery.

A generic shark, then, must wait 8-20 years just to reach sexual maturity, then additionally nurture their young internally for a year or more. After 9-21 plus years of life, a female then may produce only 4-10 young which will have to wait another 9-21 years to reproduce. If a population reaches critically low levels, it may take decades, rather than years, to return it to its former level of abundance, even if a total ban on harvesting is enforced. Bony fishes, by contrast, usually reach early sexual maturity, often at 2-3 years of age, and reproduce using external fertilization. Thousands to millions of eggs and sperm are released into the water, which develop into thousands of larvae, young and adult fishes. Of course, along the way, many die or are eaten, but the large number of progeny generated potentially facilitates the relatively quick replenishment of a population since even a few fish can produce many young that will soon reach maturity themselves and reproduce.

MANAGEMENT PROBLEMS

Management of western North Atlantic shark populations is a biologically complex and politically sensitive task. Unlike many other managed U.S. fisheries which address a single species (eg. redfish, king mackeral, striped bass, red snapper), almost 40 species of sharks are involved in the harvest. Although it is patently clear that different strategies are needed for management of individual species because of differing life history characteristics, the group is being managed as a whole. Biological and population information is largely lacking for many species. Unfortunately there is little time available for prolonged additional study, because sharks populations are so clearly impacted at this time. A U.S. National Marine Fisheries Service (NMFS) management plan aimed at reducing catches, both sport and commercial, was developed to address this pressing problem. Although the initial recovery plan was imperfect in design and grossly over-optimistic, it has been periodically adjusted as new biological and fishery data became available. Continued refinement of the plan will be required as we gain more knowledge about individual species' biology and the fishery.

THE NMFS PLAN

The NMFS shark management plan covers the Exclusive Economic Zone (EEZ), the area from 200 miles offshore inward to state waters. The NMFS plan was created in 1993 and is based on management of 39 species relegated to three species groups:

1) large coastal species, made up of the major sport and commercial target species, including the sandbar, blacktip, dusky, spinner (Carcharhinus brevipinna), silky (Carcharhinus falciformis), bull (Carcharhinus leucas), bignose (Carcharhinus altimus), narrowtooth (Carcharhinus brachyurus), Galapagos (Carcharhinus galapagensis), night (Carcharhinus signatus), reef (Carcharhinus perezi), tiger, lemon, sand tiger, bigeye sand tiger (Odontaspis noronhai), nurse, scalloped hammerhead (Sphyrna lewini), smooth hammerhead (Sphyrna zygaena), great hammerhead (Sphyrna mokarran), white (Carcharodon carcharias), basking (Cetorhinus maximus), and whale (Rhincodon typus) sharks.

2) small coastal species, consisting largely of small nearshore species, caught primarily by sportsfishers and as by-catch of shrimp, longline and gillnet fisheries; includes Atlantic and Caribbean sharpnose (Rhizoprionodon terraenovae, Rhizoprionodon porosus), blacknose (Carcharhinus acronotus), finetooth (Carcharhinus isodon), smalltail (Carcharhinus porosus), bonnethead (Sphyrna tiburo), and angelsharks (Squatina dumeril). 3) pelagic species, a group composed of offshore and deepwater species that are harvested primarily as by-catches of tuna and swordfish longline fisheries, and are targeted by sport fishers; includes the longfin and shortfin makos (Isurus paucus, Isurus oxyrinchus), porbeagle (Lamna nasus), common and bigeye threshers (Alopias vulpinus, Alopias superciliosus), oceanic whitetip (Carcharhinus longimanus), blue (Prionace glauca), bigeye six- and sixgill (Hexanchus vitulus, Hexanchus griseus), and sevengill (Heptranchias perlo) sharks.

During the creation of the 1993 Fishery Management Plan (FMP), the NMFS determined that small coastal sharks were not over-fished and had a maximum sustainable yield (MSY) of 3,600 metric tons (mt). It also determined that pelagic sharks were well fished, but not over-fished, and had a MSY of 2,800 mt. Large coastal sharks, however, were substantially over-fished and over their MSY of 3,400 mt. In 1989 the large coastals were judged to have been over-fished by 2,348 mt and in 1990 by 1,431 mt. In 1993 he NMFS set annual poundage quotas, called total allowable catches (TAC's), for each of the heavily fished groups. The TAC for large coastals was set at 2,436 mt plus a 464 mt recreational quota, and 1,560 mt for for pelagics. No restrictions were placed on small coastal sharks. Large coastal shark's TAC's were to be adjusted annually upward at 80% of the annual surplus production. This strategy was predicted to allow for a population increase leading to a return of the natural MSY by the year 2000. Sport fishers were restricted to two sharks per boat per trip for combined large coastals and pelagics, and five sharks per person per day for small coastals. Sale of recreationally-caught sharks was prohibited. A 66" fork length (= 6 foot total length) minimum size was placed on makos. "Finning" of sharks was prohibited for both commercial and sport fishermen. In addition, a system of data collection and reporting system was partially implemented. While noble in intent, the plan vastly underestimated the recovery of the stocks. Increased awareness of this shortcoming was made through efforts of the scientific and conservation communities, resulting in subsequent modifications to the original plan.

An early addition to the plan was the institution of a 4000 pound per trip limit, which was prompted by "sweepstakes" style fishing during the first regulated year (1993). This resulted in a closure of the fishery early in each fishing season and disproportionate geographical catches influenced by seasonal migratory patterns of major shark species. Expected annual increases in large coastal TAC's were quickly scrapped as evidence clearly demonstrated that further reductions, not increases, were in order. The FMP also asked for annual evaluations of available information on stock size and landings.

The first of these evaluations occurred in 1994, at which point it was decided that the initial plan to increase the total allowable catch (TAC), should not be implemented. For that reason the quotas remained at the 1994 level of 2,570 mt. It was also determined that there was not enough new information to have another evaluation in 1995 (NMFS, 1996).

The second Shark Evaluation Workshop was conducted in 1996, to determine the status of the large coastal shark stocks. Although management had been in place for three years, the slow life history patterns of sharks made it nearly impossible to determine the effect of these plans on large coastal sharks. Results from the analysis of catch rates indicated that several of the large coastal shark species' (sandbar, dusky, hammerheads, tiger, sand tiger, silky and night) Catch Per Unit Efforts (CPUE's) had declined by over 50% from the 1970's to mid 1980's. However they could not show statistically the effects of the 1993 management plan. Despite this, it was determined that reducing fishing mortality by 50% would aid in the recovery process. In accordance, the large coastal shark quota was reduced to 1,285 mt, the recreational bag limit was reduced to two large coastal, small coastal and pelagic sharks combined per trip and two Atlantic sharpnose sharks as well. A quota of 1,760 mt was created for the small coastal shark complex and five species, great white (Carcharodon carcharias) sand tiger (Odontaspis taurus), basking (Cetorhinus maximus), whale (Rhincodon typus) and bigeye sand tiger (Odontaspis noronhai), were placed on a prohibited species list. Shortly after these regulations were put into effect, NMFS was sued by the Southern Offshore Fishing Association (SOFA). This would be the first of several lawsuits aimed at NMFS by the commercial fishing industry (NMFS, 1996). Amendments to the Magnuson-Stevens Fishery Conservation and Management Act in 1996 (modifications for definitions of over-fishing, new national standards to stop over-fishing, minimizing by-catch and by-catch mortality and identifying and protecting essential fish habitats) lead to NOAA Fisheries beginning the process of creating a rebuilding plan for large coastal sharks.

In 1998 another Shark Evaluation Workshop was held to go over the most recent catch and landings data. The results of these evaluations indicated that the large coastal shark complex needed further reductions in fishing mortality, while the sandbar catch rate may be sustainable. In 1999 the Highly Migratory Species division of NMFS published a new shark FMP (which combined sharks, billfish and tuna). Within this FMP, the large coastal group was broken into the ridgeback and non-ridgeback group, each with its own quota (a reduced version of the 1996 quota) and a minimum size limit, a commercial quota for blue sharks, species-specific quota for porbeagle sharks and a reduced pelagic shark commercial quota. The recreational limit was reduced and the commercial fishery became a limited access fishery. Dead discards and state landed sharks were counted against the Federal quota after the season closure and over and under usage of the quota could be added/subtracted from the next season. In addition to all of these plans, 14 additional species were placed on the prohibited species list.

The new regulations were put into place in May of 1999. In June of the same year, a court order based on the first SOFA lawsuit stopped the implementation of new quotas and fish counting methods. Following the release of the 1999 FMP, the NMFS was sued again by SOFA over the new measures, and was ordered by a judge to have independent reviewers look at the 1998 stock assessment.

The independent reviewers concluded that the conclusions made following the 1998 stock assessment were not based on the best scientific information available or proper stock assessment techniques. The result of the lawsuit and reviews was a reduction in large coastal and small coastal quotas back to the 1997 limit, not counting the dead discards and state catches against the quota, and the removal of size limits.

The most recent Shark Evaluation Workshop occurred in 2002. The stock assessments that resulted from this meeting show that the large coastal aggregate is over-fished and over-fishing is still occurring, sandbar sharks are no longer over-fished but that over-fishing is still occurring and that blacktip shark stocks are rebuilt and over-fishing is no longer occurring. Four extra years of data and new biological information were added to this assessment. This stock assessment was also reviewed by independent reviewers, who returned much more favorable results and comments. After this assessment, an emergency rule went into effect creating a separate quota for ridgeback (783 mt) and non-ridgeback (931 mt) species, counting dead discards and state landings against the quota and season-specific quota adjustments. During 2002, the first two small coastal shark assessments since 1992 were submitted to NMFS. These both indicated that the finetooth sharks were being over-fished and that over-fishing was occurring, however the Atlantic sharpnose, bonnethead, and blacknose shark are not over-fished and over-fishing is not occurring.

Currently the HMS FMP for sharks is being revised and amended. Scientists, fishermen and conservationists have been working for years to create a plan that would allow fishermen to sustainably fish these long-lived animals. Scientific research and the collection of both biological and fishery data must continue to be collected in order for these goals to be achieved.