Hybridization between closely related species has been documented across a wide range of taxa but has not been well studied in elasmobranchs. Hammerhead sharks have drawn global conservation concern because they experience some of the highest mortality rates among sharks when interacting with fisheries. Here we report on the detection of hybrids between the globally distributed scalloped hammerhead ( Sphyrna lewini ) and recently described Carolina hammerhead ( S. gilberti ) which are only known from the western Atlantic Ocean. Using a genomics approach, 10 first-generation hybrids and 15–17 backcrosses were detected from 554 individuals. The identification of backcrosses demonstrates hybrids are viable, and all backcrosses but one involved a scalloped hammerhead. All hybrids but one possessed Carolina hammerhead mtDNA, indicating sex-biased gene flow between species. Repeated hybridization and backcrossing with scalloped hammerheads could lead to the loss of endemic Carolina hammerheads.

For species that do not provide parental care after birth, excess maternal provisioning during development, beyond what is required for embryogenesis, provides offspring with resources to increase their chances of survival. Maternally derived resources are expected to be important for buffering offspring against limited food resources at birth or time needed to learn how to properly feed. Young-of-the-year (YOY) cryptic Scalloped Hammerheads (Sphyrna lewini) and Carolina Hammerheads (Sphyrna gilberti) were sampled from nurseries along the US Atlantic Coast and compared for a number of biological condition metrics across three developmental stages. Large declines in liver lipid content and hepatosomatic indices were found in neonatal sharks, using umbilical scar healing as a proxy for time since birth. Feeding commenced quickly as 96% of sharks had prey remnants in their stomachs. The combination of rapid exhaustion of maternally provided resources and high occurrence of stomachs with prey contents indicate that nursery quality, with respect to prey availability, may be important for YOY hammerhead survivorship. While externally the two species are morphologically similar, longer length-at-birth in S. lewini and higher hepatic condition in neonatal S. gilberti suggest that aspects of reproductive biology, including physiology, may differ between species. While more information is needed to distinguish life history differences between these two species, data collected from YOY may serve as a useful proxy to inform management when adult samples of cryptic species are difficult to collect.

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In California, recreational fisheries contribute a significant amount to coastal economies, with pelagic and coastal pelagic species constituting a principal set of target species during summer and fall. Although traditional catch frequency (landings) data sets exist for these species, size‐specific information is limited, especially for the largest size‐classes. We digitized weekly records of trophy catch reported in the “Whoppers of the Week” section of the Western Outdoor News, a California fishing and hunting newspaper published since 1953. The resulting database contained catch records that described the largest fish caught at each sportfishing landing site along the California coast during 1966–2013. We then assessed the temporal dynamics in trophy size of the top‐15 pelagic and coastal pelagic species, with a combined total of 21,440 individual catch records. Among the 15 pelagic and coastal pelagic species examined, the Yellowfin Tuna Thunnus albacares and Striped Bass Morone saxatilis were the only species that showed clear long‐term declines in trophy size over the study period, whereas the Pacific Bluefin Tuna Thunnus orientalis, White Seabass Atractoscion nobilis, and Yellowtail Jack Seriola lalandi exhibited long‐term increases in size. In general, the trophy sizes of pelagic species were more variable than those of coastal pelagic species and were not as consistently correlated with oceanographic conditions; both findings likely reflect the fact that oceanography drives the availability but not necessarily the size of pelagic species catch. In contrast, coastal pelagic species demonstrated trends in trophy sizes that were more consistently responsive to both oceanography and fisheries management. Our results suggest that oceanographic processes, natural history characteristics, fishing, and fisheries regulations each play a role in trophy size dynamics, but their relative influences vary among species. Received December 12, 2015; accepted April 26, 2016Published online August 3, 2016

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Two sharks, visually identified in the field as young-of-the-year (YOY) scalloped hammerhead Sphyrna lewini, were identified as great hammerhead Sphyrna mokarran based on nuclear-encoded single nucleotide polymorphisms (SNP) and sequences of mtDNA. Individuals were captured and released in Bulls Bay, SC, and Saint Joseph Bay, FL, in 2013 and 2014, respectively. These findings indicate S. mokarran may be pupping in or around these areas and highlight new regions that may be a productive focus for future research on early life history of S. mokarran.

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Examination of 32 spiral valves from neonate specimens of hammerhead shark Sphyrna spp. (Carcharhiniformes: Sphyrnidae) captured between June and August 2018 off the Atlantic coast of South Carolina, USA, revealed the presence of the capillariid nematode Piscicapillaria bursata (Capillariidae) in the Carolina hammerhead S. gilberti, the scalloped hammerhead S. lewini, and their hybrids. This is the second find of this parasite originally described from hammerhead sharks off Australia, its first record from the western Atlantic Ocean, and its first record in a new host species and in hybrids.