Pity the pandalid shrimp. Fisheries not only harvest this cold-water crustacean in ever growing numbers but also ignore critical details of its life cycle. Pandalid shrimp are protandric hermaphrodites: all juveniles develop testicular tissues and spawn by releasing sperm into the water for external fertilization. Each shrimp can live for up to five years, and during breeding seasons hormonal changes can transform the animal into an egg-bearing female.
An individual usually becomes a female once it has reached a threshold body size. If there are too many males or females in a given year, however, an individual will often spawn as a member of the rarer sex, keeping the sex ratio balanced. Males “choose” to stay male or become female during the “maturing season” of early summer.
With autumn's arrival, the window of opportunity to change sex closes. The shrimp breed and are harvested using traps that retain only large specimens—that is, only females. A study in the Journal of Animal Ecology confirmed that those left behind are mostly male, thus erasing the benefits of sex swapping.
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These skewed sex ratios cripple the species' reproductive capacity for each breeding season. Worse yet, smaller females are less fertile than large ones, meaning the few remaining females have suboptimal reproductive rates.
The study's authors suggest a simple solution. If harvest season were moved from fall to spring, before the shrimp's summer sex changes, postharvest populations would have time to adjust for the lack of females. This approach could help ensure sustainable fisheries—and a more continuous supply of shrimp cocktail.