Are there long-term temporal trends of size composition and the length– weight relationship? Results for chokka squid Loligo reynaudii during the peak spawning season off the south coast of South Africa

Temporal trends in the size composition (length frequency) and length–weight (L–W) relationship of chokka squid Loligo reynaudii on the south coast of South Africa were assessed over periods spanning 22 years: length frequencies from 1996 to 2017 (with 15 years  represented); and L–W relationships over 9 years between 1994 and 2016. To allow for comparison, identical data selection and processing was adopted for all years considered (i.e. identical period of 60 days in spring–summer; the same depths and areas; chokka with empty stomachs; and squid of the same maturity stage). Although there were no significant long-term temporal trends in the mean lengths, there was a significant short-term drop in the mean lengths over the years 2014–2017 (especially in females), which could not be attributed with certainty to any cause. A tentative explanation is that this drop might be linked to the introduction of an additional closed season in these years. The estimated parameters of the L–W relationship also revealed no trend over the years considered. Investigation of the caecum colour, which indicates the state of starvation (white: 8 h on average after food ingestion; yellow: 6 to 7 h after food ingestion), showed significantly more starving males than starving females. Starvation of males on the spawning grounds might be associated with the spawning behaviour of chokka

Age estimates of chokka squid Loligo reynaudii off South Africa and their use to test the effectiveness of a closed season for conserving this resource

This study presents age distributions in an exploited population of spawning chokka squid Loligo reynaudii together with their back-calculated spawning times, and considers the results in relation to the exploitation of this species. Samples were collected during two closed fishing seasons, in 2003 and 2004. Age after hatching ranged, in males, from 168 to 484 days, with a mean of 323 days (71–425 mm mantle length [ML]), and in females from 125 to 478 days, with a mean of 316 days (83–263 mm ML). Detailed analysis of catches during nine days of fishing after the end of the closed season indicated strongly that the closed season (October–November) has been beneficial for both the chokka resource and the fishery. The temporal distribution of egg-laying events for parental populations, and a high abundance of squid in the days immediately after the end of the closed season, indicate a link between the parental spawning stock and the resulting spawning stock. This hypothesis was formulated using the  distribution of egg-laying events in time, the strength of egg-laying events, and data for the daily catch immediately (i.e. nine days) after the closed season. However, the hypothesis requires rigorous testing using statoliths collected over a longer period. Keywords: age distribution, catch pattern, commercial jig catches, egg-laying date, statoliths, stock–recruitment relationshi

South Africa

The world's climate is changing more rapidly than scientists had envisioned just a few years ago, and the potential impact of climate change on world food production is quite alarming. Nowhere is the sense of alarm more keenly felt than among those who study the warming of the world's oceans. Evidence of the dire effects of climate change on fisheries and fish farming has now mounted to such an extent that the need for a book such as this has become urgent. A landmark publication devoted exclusively to how climate change is affecting and is likely to affect commercially vital fisheries and aquaculture operations globally, Climate Change Impacts on Fisheries and Aquaculture provides scientists and fishery managers with a summary of and reference point for information on the subject which has been gathered thus far. Covers an array of critical topics and assesses reviews of climate change impacts on fisheries and aquaculture from many countries, including Japan, Mexico, South Africa, Australia, Chile, US, UK, New Zealand, Pacific Islands, India and others Features chapters on the effects of climate change on pelagic species, cod, lobsters, plankton, macroalgae, seagrasses and coral reefs Reviews the spread of diseases, economic and social impacts, marine aquaculture and adaptation in aquaculture under climate change Includes special reports on the Antarctic Ocean, the Caribbean Sea, the Arctic Ocean and the Mediterranean Sea Extensive references throughout the book make this volume both a comprehensive text for general study and a reference/guide to further research for fisheries scientists, fisheries managers, aquaculture personnel, climate change specialists, aquatic invertebrate and vertebrate biologists, physiologists, marine biologists, economists, environmentalist biologists and planners

Cryptic biodiversity in the commercial diamondback squid Thysanoteuthis rhombus Troschel 1857

21 pages, 4 figures, 3 tables, supplementary information https://doi.org/10.1007/s11160-023-09813-3.-- Data availability: Alignments and raw data generated can be found in FigShare (https://doi.org/10.6084/m9.figshare.22559374). All the new sequences generated here are in the National Center for Biotechnology Information (NCBI) database under the GenBank accession numbers OP970836-OP970872 (cytochrome oxidase c subunit I.), OP970877-OP970912 (16S ribosomal RNA), and OP971221-OP971257 (12S ribosomal RNA)Cephalopod fisheries are increasing, but little is known about the cryptic diversity of some key commercial species. Recent studies have shown that cryptic speciation is common in cephalopods, including several oceanic squids formerly considered ‘cosmopolitan species.’ Further efforts are needed to investigate the cryptic diversity of commercial species, to inform management and support sustainable fisheries practices. Thysanoteuthis rhombus is an oceanic squid, currently recognized as the single species of the family Thysanoteuthidae. Thysanoteuthis. rhombus has a global distribution in tropical and subtropical waters and is an economically important species, with the highest catches occurring off Okinawa in Japan and of potential fishery resource for other countries due to its high abundance and large size. Here, we used sequences from 12S rRNA, 16S rRNA, and cytochrome c oxidase I to characterize its cryptic diversity using samples collected throughout most of its known geographic range. We identified three different putative species whose distributions are concordant with main ocean basins: Thysanoteuthis major, the most abundant species, is widely distributed in the North Pacific Ocean, North Indian Ocean, and limits of the South Atlantic Ocean; Thysanoteuthis rhombus is distributed in the North and South Atlantic Ocean and Mediterranean Sea; and Thysanoteuthis cf. filiferum, likely the least sampled to date, is found in the southwestern Pacific Ocean. A sister relationship was observed between T. rhombus and T. major, and T. cf. filiferum was found to be the most divergent species. Based on our divergence estimation, we hypothesize that the closure of the Isthmus of Panama during the early Pliocene played a significant role in the split of T. rhombus and T. major, while the split of their ancestor from T. cf. filiferum coincided with an increase in the Pacific Walker Circulation and the longitudinal gradient of surface temperatures in the Pacific Ocean during the Late Oligocene and Early Miocene. Our work identifies three different putative species within Thysanoteuthis and has potential use for improving fishery management and conserving the diversity in these speciesD.D. was supported by The Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) fellowship. G.S. wants to thank the support of the 22K15085 Grant-in-Aid for Early-Career Scientists (KAKENHI). F.Á.F.-Á. was supported by a JdC-I Postdoctoral Fellowship Grant (ref. IJC2020-043170-I) awarded by MCIN/AEI https://doi.org/10.13039/501100011033, by a Beatriu de Pinós fellowship from Secretaria d'Universitats i Recerca del Departament de Recerca i Universitats of the Generalitat de Catalunya (Ref. BP 2021 00035), the project ECOPHYN (Ref. PID2021-126824NB-C32, Ministerio de Ciencia e Innovación, Gobierno de España) and the European Union and the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). A.E was supported by a Margarita Salas Postdoctoral Fellowship Grant awarded by Ministry of Universities of Spanish government and is thankful to the support of project DEEPCOM (Ref. CTM2017-88686-P, Ministerio de Ciencia e Innovación, Gobierno de España). We are thankful to the Director of ICAR-CMFRI, Kochi, India for facilities and support. CH. S. is thankful to the support of the JSPS KAKENHI Grant-in-Aid for Early-Career Scientists, Grant Number 19K15901Peer reviewe

Beta diversity of rock-restricted cichlid fishes in Lake Malawi: importance of environmental and spatial factors

The rock-restricted cichlid fish assemblages of Lake Malawi exhibit high spatial diversity in their species composition and relative abundance. However the extent to which this is due to the effects of local environmental differences, dispersal limitation of constituent taxa, and the assignment of allopatric populations to species is uncertain. We examined the factors associated with diversity within an assemblage from the north-western shores, encompassing a spatial scale of 170 km. For both the whole assemblage, and all constituent species-complexes, spatial variance in community structure was significantly dependent upon both geographic distances between locations and local habitat variables. Pronounced effects of distance indicate limited dispersal, but our results also show that that the spatial variance explained by geographic distance alone was strongly linked to proportion of allopatric populations within a species-complex with species status. Thus, the taxonomic status of allopatric populations underlies, at least partially, the biogeographical structure of this assemblage. Substrate composition and habitat depth were also significant determinants of community structure, although spatial variance attributed to these variables was less than that associated with distance alone. Substantial unexplained variance may be a consequence of the effects of unmeasured habitat variables, high ecological similarity between co-occurring species, stochastic influences on population abundance, and the effects of local adaptation. Despite low spatial variance explained by the assessed environmental variables, significant environmental influence on cichlid assemblage structure across a wide spatial scale indicates that even slight future environmental changes may have the capacity to significantly alter species composition

Quantifying the impact of environmental factors on arthropod communities in agricultural landscapes across organizational levels and spatial scales

1. In landscapes influenced by anthropogenic activities, such as intensive agriculture, knowledge of the relative importance and interaction of environmental factors on the composition and function of local communities across a range of spatial scales is important for maintaining biodiversity. 2. We analysed five arthropod taxa covering a broad range of functional aspects (wild bees, true bugs, carabid beetles, hoverflies and spiders) in 24 landscapes (4 x 4 km) across seven European countries along gradients of both land-use intensity and landscape structure. Species-environment relationships were examined in a hierarchical design of four main sets of environmental factors (country, land-use intensity, landscape structure, local habitat properties) that covered three spatial scales (region, landscape, local) by means of hierarchical variability partitioning using partial canonical correspondence analyses. 3. Local community composition and the distribution of body size classes and trophic guilds were most affected by regional processes, which highly confounded landscape and local factors. After correcting for regional effects, factors at the landscape scale dominated over local habitat factors. Land-use intensity explained most of the variability in species data, whereas landscape characteristics (especially connectivity) accounted for most of the variability in body size and trophic guilds. 4. Synthesis and applications. Our results suggest that management effort should be focused on land-use intensity and habitat connectivity in order to enhance diversity in agricultural landscapes. Since these factors are largely independent, specific conservation programmes may be developed with regards to socio-economic and agri-environmental requirements. Changes in either of these factors will enhance diversity but will also result in specific effects on local communities related to dispersal ability and the resource use of species

Diversity and community composition of butterflies and odonates in an ENSO-induced fire affected habitat mosaic: a case study from East Kalimantan, Indonesia

Little is known about the diversity of tropical animal communities in recently fireaffected environments. Here we assessed species richness, evenness, and community similarity of butterflies and odonates in landscapes located in unburned isolates and burned areas in a habitat mosaic that was severely affected by the 1997/98 ENSO (El Nin˜o Southern Oscillation) event in east Kalimantan, Indonesian Borneo. In addition related community similarity to variation in geographic distance between sampling sites and the habitat/vegetation structure Species richness and evenness differed significantly among landscapes but there was no congruence between both taxa. The species richness of butterflies was, for example, highest in sites located in a very large unburned isolate whereas odonate species richness was highest in sites located in a small unburned isolate and once-burned forest. We also found substantial variation in the habitat/vegetation structure among landscapes but this was mainly due to variation between unburned and burned landscapes and variation among burned landscapes. Both distance and environment (habitat/vegetation) contributed substantially to explaining variation in the community similarity (beta diversity) of both taxa. The contribution of the environment was, however, mainly due to variation between unburned and burned landscapes, which contained very different assemblages of both taxa. Sites located in the burned forest contained assemblages that were intermediate between assemblages from sites in unburned forest and sites from a highly degraded slash-and-burn area indicating that the burned forest was probably recolonised by species from these disparate environments. We, furthermore, note that in contrast to species richness (alpha diversity) the patterns of community similarity (beta diversity) were highly congruent between both taxa. These results indicate that community-wide multivariate measures of beta diversity are more consistent among taxa and more reliable indicators of disturbance, such as ENSO-induced burning, than univariate measures