National Shark Research Consortium
Florida Program for Shark Research - Florida Museum of Natural History
Featured Projects
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NSRC Featured Project:
Reproduction of the sandbar shark (Carcharhinus plumbeus) in the northwestern Atlantic Ocean and Gulf of Mexico
The sandbar shark, Carcharhinus plumbeus, is a member of one of the largest and most commercially
important shark families (Carcharhinidae). This species is widely distributed in tropical
and subtropical regions of the Pacific, Indian, and Atlantic Oceans, as well as the Mediterranean Sea.
In North American waters, C. plumbeus ranges from Cape Cod to Florida,
throughout the Gulf of Mexico, and around Hawaii.
The sandbar shark has historically been a key species in commercial shark fisheries along the U.S. East coast.
As shark fin soup is the main drive for the commercial shark fishing industry, this species is highly sought after
for its large fins. In recent years, sandbar sharks have been heavily fished in the northwestern Atlantic,
representing 35.9% of the targeted catch in the coastal bottom long-line shark fishery.
Additionally, this species comprises approximately 20% of the large shark fauna and is second only to the blue
shark, Prionace glauca, in recreational catches along the U.S. east coast.
Despite current fishery management strategies, recent stock assessments have shown that sandbar shark populations
along the U.S. East coast have greatly declined. National Marine Fisheries Service (NMFS) scientists have
deemed the sandbar shark as over fished. To this end, NMFS has closed the sandbar shark fishery and established
a research only fishery for this species. Since the sandbar shark represents such a large portion of the
commercial catch for the bottom long-line fishery, this action has severely impacted the bottom long-line fishery.
Pre-ovulatory ovary with developed eggs (left) / Inactive ovary without developing eggs (right)
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This decline in sandbar shark populations reinforces the need for improved data on the biology of commercially
important shark species. More accurate assessment models, developed with updated life history data
(age, growth, and reproduction), will allow fisheries managers to establish more reliable catch quotas
to ensure future sustainability of the fishery. To this end, FPSR scientists are studying the reproductive
biology of the sandbar shark in the northwestern Atlantic Ocean and Gulf of Mexico. This study is focused
on characterizing reproductive parameters including the size of maturity, fecundity, length of gestation,
timing of reproductive events, and how often mature female sandbar sharks reproduce. These data allow for
estimation of reproductive output, a parameter used in assessment models.
Close up of an early term embryo, approximately 3-4 weeks into gestation (left) / Near term embryo (right)
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Sharks specimens used in this study were obtained through fishery-dependent and -independent sampling utilizing
bottom long-line fishing gear. Upon capture, sharks were measured for fork length and total length and clasper
lengths, and the sex of the specimen was recorded. Gonads and genital ducts were dissected in the field and
preserved for later analysis. Clasper length data was used to determine the size of mature male sharks.
Increases in nidamental gland width and the condition of the uterus were used to determine the sizes of
maturity for female sharks. Variation in the sizes of the gonads and genital ducts were used to assess the
seasonality of reproduction and to determine the timing of reproductive events such as egg development,
ovulation, sperm development and gestation.
This study is ongoing, but some preliminary results are listed below.
- Male shark produce sperm in the spring and mating occurs in early summer.
- Egg development occurs in the spring with ovulation occurring in the summer.
- The average litter size was 9.65 embryos.
- No relationship between maternal length and litter size was detected.
- The duration of gestation is 11 to 12 months.
- Females exhibit a protracted reproductive cycle. While previous studies have suggested that female sandbar sharks reproduce every other year, our results indicated that the rest period between reproductive events is longer, i.e. females may reproduce every third year or longer.
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