Sharks, rays and abortion: The prevalence of capture-induced parturition in elasmobranchs

Abstract

The direct impacts of fishing on chondrichthyans (sharks, rays and chimeras) are well established.Here we review a largely unreported, often misinterpreted and poorly understood indirect impact of fishing on these animalscapture-induced parturition (either premature birth or abortion). Although direct mortality of discarded sharks and rays has been estimated, the prevalence of abortion/premature birth and subsequent generational mortality remains largely unstudied. We synthesize a diffuse body of literature to reveal that a conservative estimate of > 12% of live bearing elasmobranchs (n = 88 species) show capture-induced parturition. For those species with adequate data, we estimate capture-induced parturition events ranging from 2 to 85% of pregnant females (average 24%). To date, capture-induced parturition has only been observed in livebearing species. We compile data on threat-levels, method of capture, reproductive mode and gestation extent of premature/aborted embryos. We also utilise social media to identify 41 socialmedia links depicting a capture-induced parturition event which provide supplementary visual evidence for the phenomenon. The mortality of embryos will have implications for elasmobranch populations, and there are limited options to deal with this problem. This review is the first to synthesize available data on capture-induced parturition in sharks and rays, and highlights an important ethical and management issue for fishers and managers deserving of much greater attention.Table 1 List of terms and definitions as referred to in this review. List of definitions Stress-induced parturitionThe premature birthing of offspring stimulated by physiological processes which involve a response to a 'stressor' via complex pathways modulated by hormones. Captureinduced parturitionThe birthing of offspring prompted by interaction with fishing gear. The pathways stimulating birth are expected to vary and could be caused by interactions between physical trauma and physiological stress. Premature birthThe parturition of pre-term offspring, which often have reduced fitness due to lack of development and smaller body size. AbortionThe termination of a pregnancy by the expulsion of a foetus or embryo before it can survive outside the uterus. SharkShark generally refers to those elasmobranchs with gill slits located laterally and includes all the nine orders of chondrichthyans that are not deemed skates, rays or chimeras: sawsharks (Pristiophoriformes), angel sharks (Squatiniformes), dogfish (Squaliformes), sixgilled sharks (Hexanchiformes), mackerel sharks (Lamniformes), ground sharks (Carcharhiniformes), carpetsharks (Orectolobiformes), bullhead sharks (Heterodontiformes) and bramble sharks (Echinorhiniformes). RayRay generally refers to the three orders of chondrichthyans that are not deemed sharks, skates or chimeras. All rays are live-bearing and have gill slits that are located ventrally: stingrays (Myliobatiformes), electric rays (Torpediniformes) and shovelnose rays/guitarfish (Rhinopristiformes). SkateS...

Impacts of fisheries on elasmobranch reproduction: high rates of abortion and subsequent maternal mortality in the shortnose guitarfish

“…The most significant impact due capture stress during the reproductive period is capture-induced birth or abortion, characterized by premature expulsion of an embryo (Adams et al, 2018), which could be confirmed by our results. This process has been reported to be common in numerous viviparous species at different stages of development resulting from capture and handling (Zagaglia et al, 2011;Schluessel, Giles & Kyne, 2015;Adams et al, 2018). However, our study brings the first detailed report combined with physiological alterations related to the phenomenon in an elasmobranch.…”

“…Viviparous elasmobranchs are potentially vulnerable to reproductive disruptions of capture stress since their relatively long gestation periods increase the probability of post-release mortality or sublethal reproductive effects being caused by fishing while pregnant (Adams et al, 2018). The most significant impact due capture stress during the reproductive period is capture-induced birth or abortion, characterized by premature expulsion of an embryo (Adams et al, 2018), which could be confirmed by our results. This process has been reported to be common in numerous viviparous species at different stages of development resulting from capture and handling (Zagaglia et al, 2011;Schluessel, Giles & Kyne, 2015;Adams et al, 2018).…”

Ultrasonography as a promising methodology to indicate captured‐induced abortion in viviparous elasmobranchs

“…A particularly concerning consequence of stress during the reproductive period is abortion, characterized by the spontaneous expulsion of an embryo before it is sufficiently developed to survive (Adams et al ., ). This type of trauma has already been reported for many viviparous elasmobranch species, with involuntary embryo loss at different stages of development because of capture and handling (Adams et al ., ; Rincon, ; Schluessel et al ., ; Zagaglia et al ., ). Thus, a better understanding of possible abortion consequences due to stress of capture is of utmost importance to understand potential effects on reproduction and recruitment in the following year and to develop successful conservation and sustainable management programs.…”

“…Viviparous elasmobranchs are particularly vulnerable to capture‐induced reproductive disruptions since their relatively long gestation periods increase the probability of post‐release mortality or reproductive consequences for females caught while pregnant (Adams et al ., ; Guida et al ., ). A particularly concerning consequence of stress during the reproductive period is abortion, characterized by the spontaneous expulsion of an embryo before it is sufficiently developed to survive (Adams et al ., ). This type of trauma has already been reported for many viviparous elasmobranch species, with involuntary embryo loss at different stages of development because of capture and handling (Adams et al ., ; Rincon, ; Schluessel et al ., ; Zagaglia et al ., ).…”

“…Viviparous elasmobranchs are particularly vulnerable to capture‐induced reproductive disruptions since their relatively long gestation periods increase the probability of post‐release mortality or reproductive consequences for females caught while pregnant (Adams et al ., ; Guida et al ., ). A particularly concerning consequence of stress during the reproductive period is abortion, characterized by the spontaneous expulsion of an embryo before it is sufficiently developed to survive (Adams et al ., ).…”