Spawning aggregations of fish in Cabo Delgado, Northern Mozambique: An interview-based survey of artisanal fishers

Seasonal aggregations at specific sites are common among some fish species. Experienced fishermen know where and when these aggregations happen, often targeting these spawning sites to increase their catch. This strategy can further contribute to endangering the survival of these species, especially for those already threatened by other forms of pressure. This study contributes knowledge to the spawning aggregation of fish in the north of Mozambique following survey work conducted around Cabo Delgado Province in six coastal villages in 2016, 2017 and 2018. The objectives of the study were 1) to identify the species and sites of spawning aggregation and 2) to determine the timing of spawning aggregations. Data collection consisted of interviews targeting the most experienced fishermen to obtain information on these subjects. The results indicate that out of 124 fishermen interviewed, 59% had knowledge of spawning aggregations. The information collected from fisher interviews revealed that there are at least six spawning locations and at least eight species aggregate to spawn (Leptoscarus vaigensis, Lethrinus harak, Lethrinus nebulosus, Lethrinus obsoletus, Lethrinus olivaceus, Plectorhinchus gaterinus, Plectorhinchus schotaf, Siganus sutor). Only Siganus sutor was reported to spawn in at least one of the fishing areas used by every village. The timing of spawning aggregations most reported by fishermen was during the Kusi (South) monsoon period.

Modelling pulse fishery systems in data-limited situations

Per-recruit models have been widely used since the onset of modern fisheries science, particularly in data-limited situations. When the study fishery is a pulse fishery, namely a fishery operating over a brief period followed by a long fallow period, exploitation rates rather than fishing mortality rates are employed to calculate per-recruit quantities. The literature suggests that a discrete per-recruit model is more appropriate than a continuous per-recruit model when per-recruit quantities are expressed as a function of exploitation rates. For this reason, Erisman et al. [Erisman, B. E., Grüss, A., Mascarenas-Osorio, I., Lícon-González, H., Johnson, A. F., and López-Sagástegui, C. 2020. Balancing conservation and utilization in spawning aggregation fisheries: a trade-off analysis of an overexploited marine fish. ICES Journal of Marine Science, 77: 148–161.] recently developed a discrete per-recruit model to examine the impacts of altering exploitation rates for the Gulf corvina (Cynoscion othonopterus) pulse fishery. Using Erisman et al.’s (Erisman, B. E., Grüss, A., Mascarenas-Osorio, I., Lícon-González, H., Johnson, A. F., and López-Sagástegui, C. 2020. Balancing conservation and utilization in spawning aggregation fisheries: a trade-off analysis of an overexploited marine fish. ICES Journal of Marine Science, 77: 148–161.) data, we demonstrate in detail that, under certain conditions, it is reasonable to employ a continuous per-recruit model for a pulse fishery system. We then use the designed continuous per-recruit model to demonstrate how the timing of the pulse fishery within the year relative to the timing of reproduction can be accounted for in a per-recruit model, and we explore the impacts of these model developments. This article serves as a strong basis for future studies that model pulse fishery systems in data-limited situations.

Brachioteuthis beanii Verrill, 1881 (Cephalopoda: Brachioteuthidae) in the northwest Atlantic

Four research cruises to the Gully Marine Protected Area (known as "the Gully") off Nova Scotia, Canada (2007–2010) collected 1454 specimens of the oegopsid squid family Brachioteuthidae. All specimens were identified as Brachioteuthis beanii, and the 842 individuals collected in 2007 were used to describe the morphology and ecology of the species. A subset of 565 specimens were measured for population size distribution, and over 200 of these individuals (21–117 mm ML) were fixed, vouchered, measured, dissected, and sexed to examine the internal and external characters of juveniles, males, and females. Specimens <40 mm ML were almost entirely juveniles. Specimens 40–49 mm ML were a mix of juveniles, males, and females. The smallest specimens, where the spermatophoric complex and nidamental glands could be identified, were approximately 39 mm ML in both males and females, suggesting that maturation begins at roughly the same size in both sexes. Specimens >50 mm ML could be sexed based solely on the color and texture of the mantle. Male mantles were fusiform in shape with few small, widely spaced chromatophores and a reticulated net on the mantle that developed concurrent with the internal spermatophoric complex. Females had a flaccid mantle with larger and denser chromatophores on the mantle and head and no external ornamentation (i.e., ridges or nodules). Measurement data showed that males had slightly larger arms and wider fins than females. The high abundance of B. beanii at the Gully in August/September may be a spawning aggregation and suggests that this small squid is an important component of the canyon food web.

Reproductive biology and behavior associated with a spawning aggregation of the yellowfin grouper Mycteroperca venenosa in the US Virgin Islands

The reproductive characteristics, movement patterns and courtship behaviors associated with a yellowfin grouper (Mycteroperca venenosa, Linnaeus, 1758) fish spawning aggregation (FSA) were assessed between 2004 and 2014. The FSA was located on the Grammanik Bank, a seasonally closed area on the edge of the Puerto Rico platform, south of St. Thomas, US Virgin Islands. Fish arrived at the FSA site around full moon and departed 10–12 days after full moon (dafm), during two or three consecutive months, from January to May each year. Males were significantly larger than females and preceded females at the spawning site. Courtship coloration and behaviors showed distinct patterns relative to lunar date and time of day. Spawning was observed for several days each month in 2008, 2009, 2011 and 2014, from 6 to 10 dafm. Female gonadosomatic index (GSI) values were highest from 4 to 7 dafm. Spawning, which began at sunset, consisted of 7 to 12 males following one female along the bottom before ascending 10–20 m, then "rushing" upward to release gametes. Histological analysis of ovaries indicated females spawned every 2–3 nights, although 11.6% were capable of spawning two consecutive nights. Total spawning population size of yellowfin grouper fluctuated from 600 to 1100 fish during the study period, but consistent annual population assessments using scuba were difficult to carry out due to ocean conditions. Based on size-frequency analysis and other metrics, the M. venenosa spawning population at the Grammanik bank appears to be stable at this time with existing regulations.