Sperm limitation in the Delaware Bay blue crab population
Date
2023
Authors
Hoffman, Taylor
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Fisheries that selectively harvest based on sex and size have the potential to negatively impact the reproductive success of females in a population by causing reductions in sperm and seminal fluid transfer during mating. This study sought to determine if fisheries-induced sperm limitation is occurring in the Delaware Bay blue crab (Callinectes sapidus) population. I investigated the variation in sperm and seminal fluid quantities post-mating with respect to (1) operational sex ratio (OSR), (2) season, (3) location, (4) relative time since mating, and (5) previous spawning efforts. Mature female blue crabs were collected throughout Delaware Bay and characterized by morphological and reproductive parameters, as well as processed for sperm and seminal fluid quantities. Stored sperm quantities varied seasonally and spatially, with counts peaking in mid-mating season (mean August counts ± sd: 6.11x108 ± 4.89x108 cells/crab). OSR was positively correlated with sperm quantities, and had significant trends occurring across the 20 years trawl survey data was collected for and within the crab pot season (March - November). One order of magnitude difference in sperm count for no-brood females with clean carapaces from the upper to lower Delaware Bay regions with counts decreasing closer to the mouth suggests the crabs have potential in becoming sperm limited as they have not yet used any of their sperm stores towards spawning, impacting their brood production output early-on. Similarly, sperm quantities were an order of magnitude less between females of clean and dirty carapace conditions when they had not yet produced broods. Sperm cell viability increased overall from January through June as mating season progressed. Viability measurements allowed me to simulate my own post-mating sperm loss scenario of 30% cell loss between the time of mating and the production of the first brood. To quantify lifetime brood production and determine whether females from this study that have mated and not yet produced a brood will likely become sperm limited within the first reproductive year, I applied my most recent viability percentages (81% June ‘23) to initial post-mating sperm quantities in a brood production model. Modeling shows females with no prior brood evidence can produce 0 to 4 broods out of a maximum estimated lifetime production of 8 broods for varying post-mating sperm loss scenarios (90% loss - 0 broods; 50% loss - 0-1 broods; 30% loss - 0-2 broods; no loss - 0-4 broods), suggesting females in the population will become sperm limited in the first reproductive season. Overall, all crabs collected had mated, but variations in stored sperm quantity and OSR, as well as modeling of viability-corrected lifetime brood production indicate the Delaware Bay blue crab population has potential for sperm limitation.
Description
Keywords
Sperm limitation, Reproductive success, Bay blue crab, Brood production model