Size at maturity, reproductive cycle and fecundity of the southern California brown box crab, Lopholithodes foraminatus, and implications for developing a new targeted fishery

The brown box crab, Lopholithodes foraminatus, is a deepwater crab that is found along the eastern Pacific Coast. Historically, landings in California have been low for this species, but an increase in fishing pressure prompted the state to designate it as an emerging fishery and implement an experimental fishery program for it. With no known biological studies on brown box crab in California, gathering essential fisheries information to evaluate the feasibility of a targeted fishery is necessary. We investigated the reproductive capacity of the brown box crab in southern California. From 2018 – 2021 brown box crabs were collected monthly from fishermen. Size at sexual maturity was determined by presence/absence of mature gonads (physiological), relative growth of the chela for males and abdomen width for females (morphometric), and presence/absence of eggs on females (functional). We found that females reach physiological maturity at a carapace width between 50.8 mm and 71.7 mm, and males between 43.3 mm and 66.3 mm. Morphometric maturity analysis showed a clear inflection point of abdomen width between immature and mature females. Females were 50% functionally mature at 75 mm carapace width. Morphometric and functional maturity was not detected for males, albeit samples of small male crabs were extremely limited thus warranting further study. Females followed a biennial reproduction pattern, mating in the fall followed by an 18-month brooding period with hatching the following spring. Fecundity was positively related to size and ranged from 8,352 and 62,181 eggs per female for crabs measuring 67.8 to 130.5 mm carapace width, respectively. These findings provide biological information that can inform the evaluation of a fishery for the brown box crab, including potential management strategies and models for assessing stock condition.