Length-weight relationships of 15 mesopelagic shrimp species caught during exploratory surveys off the Canary Islands (central eastern Atlantic)

were taken for individuals collected during three research campaigns using a commercial semi-pelagic trawl net. The most represented families among the collected species were Sergestidae and Oplophoridae, with eight and three species, respectively. Overall, 60% of the species showed isometric growth, 33.3% negative allometry and 6.7% positive allometry. These 15 LWRs are the first contribution on mesopelagic shrimp species from the northwest Africa region, contributing to knowledge on the relative growth of these crustaceans.

tral eastern Atlantic) performed on board the R.V. La Bocaina.In a total of 70 biological sampling hauls, mesopelagic shrimps were caught between the sea surface and 1035 m depth.The fishing gear was a commercial semi-pelagic trawl net with 5 mm mesh size at the cod-end (for more details see Guerra-Marrero et al. 2020).

Biological sampling
Immediately after capture, shrimps were initially fixed in formaldehyde (4%) for 4 hours, and then preserved in 70% ethanol, prior to their identification to the lowest possible taxonomic level (Crosnier and Forest 1973, Zariquiey-Alvarez 1968, González-Perez 1995, Burukovskii 1992, among others).Subsequently, in the laboratory, the total length (TL) and cephalothorax length (CL) were measured to the nearest 0.01 mm using a digital calliper, and the total weight (TW) was recorded to the nearest 0.0001 g using a digital balance (Sartorious, Basic).

Length-weight relationships
The LWRs were fitted using the equation TW= aTL b (power function), where TW is the total weight, TL is the total length, a and b are the regression parameters (a, regression intercept or constant; b, regression slope or allometric coefficient) estimated by linear regression on the logarithmic-transformed data and adjusted through the least squares method.Student's t-test was used to verify the positive or negative allometry when the b value is significantly higher or lower than the isometric value (b=3).The standard error and 95% confidence interval were also estimated for the LWR parameters.
All statistical analyses were conducted using the R software (R Core Team 2023).

RESULTS
A total of 1210 specimens belonging to 15 species from 3 superfamilies (Oplophoroidea, Penaeoidea and Sergestoidea) were sampled and identified (Table 2).Five families were collected, Sergestidae being the most abundant in both number of species (eight) and individuals, following by Oplophoridae with three species.
The growth patterns of 15 species were described from the LWRs parameters (Tables 1 and 2).The mean values of the correlation coefficients were high, with a mean value of 0.944±0.0333.Systellaspis pellucida showed the worst correlation index, with a value of 0.874, while Allosergestes nudus showed the highest correlation index (R=0.994).In relation to growth, it was observed that 60% of the species analysed showed isometric growth (b=3; t-test, p>0.05), while 6.7% and 33.3% showed positive (b>3; t-test, p<0.05) or negative allometric growth (b<3; t.test, p<0.05).Allosergestes sargassi and S. pellucida showed the lowest values of the allometry coefficient range (b), while Systellaspis debilis showed the highest value.
Over the years, the estimation of mesopelagic shrimp biomass from oceanographic campaigns has been influenced by a catchability problem of the fishing gears, since the sample size is usually not very large and the DVMs can significantly affect the estimated biomass in the water column (Vereshchaka et al. 2019).Biomass is normally estimated from acoustic data and primary production studies (Irigoien et al. 2014) because the information available on the ecology and biology of these species, and particularly on growth, is very scarce.
Frequently, the lack of biological data on crustacean species with low or without fishing interest at regional level is partially compensated by using standardized data available on global databases such as SeaLifeBase.org (Palomares and Pauly 2012), where it is possible to obtain the maximum length and weight reported for some species, the depth range and the geographical distribution.However, such data are only useful for a general approach, not for establishing any particular characteristic of the species at a more local or regional level.Unfortunately, in the particular case of mesopelagic shrimps, the biological information available is almost nil in the specialized literature, particularly for the central eastern Atlantic, with the exception of a few taxonomic monographies (Zariquiey-Alvarez 1968, De Grave and Fransen 2011), first records, faunal lists and latitudinal/vertical distributions of species (Quiles et al. 2001, Muñoz et al. 2012, Vereshchaka et al. 2019 Species life-cycle parameters are required for the proper management of fishing resources, but also for estimating biomass fluxes between trophic levels and assessing the role of each group within the marine ecosystem (Couce-Montero et al. 2021).Knowledge on the length-weight relationships (LWR) can be used to gather information of species growth patterns, estimate condition index and analyse growth variations on temporal or spatial scales between populations/stocks (González- Acosta et al. 2004, Gerritsen and McGrath 2007, Froese and Pauly 2015).In this study, 15 mesopelagic shrimp species caught around the Canary Islands (central eastern Atlantic) were analysed to estimate the LWRs and analyse their relative growth patterns.

Fishing surveys
Individuals were collected during three research campaigns (Table 1) around the Canary Islands (Cen-

DISCUSSION
This study provides the first estimation of the LWRs of 15 mesopelagic shrimp species caught in several exploratory surveys carried out in the Canary Islands area (central eastern Atlantic).This is the first study that gives growth information on these mesopelagic decapod crustaceans.Biological data on these crustaceans are scarce, probably because the fishing gears used in the exploratory campaigns of this mesopelagic community make the individuals suffer a significant deterioration of their structures, because their exoskeleton and appendages are very fragile.The deterioration of these structures of high taxonomic value reduces the number of samples, so in this study only individuals that allowed a reliable taxonomic identification were included.

Table 1 .
-Names and dates of research campaigns, number of trawls and depth intervals where the mesopelagic shrimps were collected.

Table 2 .
-Length-weight relationships for mesopelagic shrimps from Canary Island waters.TL, total body length; CL, cephalothorax length; W, wet weight; CI, confidence interval; n, number of specimens analysed; ns, nonsignificant.a, b and R are the regression parameters calculated from the TL~W relationship.