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Growth, productivity, and relative extinction risk of a data-sparse devil ray
Sebastián A Pardo1, Holly K Kindsvater1,2, Elizabeth Cuevas-Zimbrón3
1Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada.
Devil rays have low population growth rates, making them vulnerable to extinction from fishing pressure. Similar to manta rays, they require comparable conservation efforts due to their low productivity and high susceptibility to mortality.
Area of Science:
- Marine Biology
- Fisheries Science
- Conservation Biology
Background:
- Devil rays (Mobula spp.) are increasingly targeted for their gill plates, yet data on their population dynamics are scarce.
- Unlike manta rays, devil rays are not listed under CITES, highlighting a gap in their international protection.
- Understanding the life history and population growth rates of devil rays is crucial for assessing their extinction risk.
Purpose of the Study:
- To estimate key life history parameters for the Spinetail Devil Ray (Mobula japanica), including growth, mortality, and age at maturity.
- To determine the maximum intrinsic population growth rate (rmax) for devil rays and compare it with other chondrichthyans.
- To evaluate the sustainability of current fishing rates on devil ray populations.
Main Methods:
- Utilized a published size-at-age dataset for Mobula japanica to calculate somatic growth rates, age at maturity, and maximum age.
- Estimated natural and fishing mortality rates.
- Calculated the maximum intrinsic population growth rate (rmax) and compared it to 95 other species of cartilaginous fishes.
Main Results:
- Larger devil ray species exhibit slow somatic growth, low reproductive output, and consequently, low maximum population growth rates, indicating low productivity.
- Estimated fishing rates from a Mexican artisanal fishery were found to be comparable to the estimated rmax, suggesting unsustainable exploitation.
- The rmax for devil rays is similar to that of manta rays, suggesting a comparable vulnerability to fishing mortality.
Conclusions:
- Devil rays possess low intrinsic productivity, making them highly susceptible to overfishing and local extinction.
- Current fishing pressures, even from small-scale fisheries, may be unsustainable for devil ray populations.
- The findings support the need for similar conservation measures and protections for both devil rays and manta rays.
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