Error Distribution Model to Standardize LPUE, CPUE and Survey-Derived Catch Rates of Target and Non-Target Species

Indices of abundance are usually a key input parameter used for fitting a stock assessment model, as they provide abundance estimates representative of the fraction of the stock that is vulnerable to fishing. These indices can be estimated from catches derived from fishery-dependent sources, such as catch per unit effort (CPUE) and landings per unit effort (LPUE), or from scientific survey data (e.g., relative population number—RPN). However, fluctuations in many factors (e.g., vessel size, period, area, gear) may affect the catch rates, bringing the need to evaluate the appropriateness of the statistical models for the standardization process. In this research, we analyzed different generalized linear models to select the best technique to standardize catch rates of target and non-target species from fishery dependent (CPUE and LPUE) and independent (RPN) data. The examined error distribution models were gamma, lognormal, tweedie, and hurdle models. For hurdle, positive observations were analyzed assuming a lognormal (hurdle–lognormal) or gamma (hurdle–gamma) error distribution. Based on deviance table analyses and diagnostic checks, the hurdle–lognormal was the statistical model that best satisfied the underlying characteristics of the different data sets. Finally, catch rates (CPUE, LPUE and RPN) of the thornback ray Raja clavata, blackbelly rosefish Helicolenus dactylopterus, and common mora Mora moro from the NE Atlantic (Azores region) were standardized. The analyses confirmed the spatial and temporal nature of their distribution.

The effect of escape gap on the cube folding trap on fish catches composition and trap rate at the northern coast of Tuban regency

This study aims to determine the effect of escape gap on catch composition, CPUE, and trap rate at the northern coast of Tuban Regency. The research was conducted by ten trips of experimental fishing at different locations in November 2019. A total of 60 units of cube folding traps were installed long line, consisting of cube folding traps without escape gaps, cube folding traps with escape gaps 6x3 cm, cube folding traps escape gaps 7x4 cm, 20 units, respectively. The fish catch composition consists of 18 species of 6 groups, i.e., fish, swimmer crab, shrimp, hermit crab, and snail. Fish were the most dominant group captured by cube folding traps in the northern coast of Tuban Regency (59.7%), followed by swimmer crab, snail, crab, shrimp, and hermit crab. The highest catch per unit effort was found in cube folding traps with escape gaps 7x4 cm as much as 6,94 gr/traps/trip. The highest of the trap rate (18%) was obtained in the cube folding traps without escape gap. There was a significant difference (p=95%) in the weight of fish catches and CPUE between cube folding traps without escape gaps and the cube folding traps with escape gaps 7 x 4 cm.

VARIASI HASIL TANGKAPAN IKAN DARI PERAIRAN SAMUDERA HINDIA, YANG DIDARATKAN DI PPN SIBOLGA PANTAI BARAT SUMATERA TAHUN 2019

Overfishing and overcapacity is a problem for the sustainability of capture fisheries development. Indonesia has experienced overfishing or called overfishing and overcapacity or called excess fishing capacity. The west coast of the island of Sumatra has enormous fishing potential, both in territorial waters and in ZEE waters. The purpose of the study was to understand the trend of fluctuations in fish catches in the waters of West Sumatra. Assessing the effect of boat trips on fish catches in the waters of West Sumatra and providing basic information and management of fisheries in the waters of West Sumatra. The research material used is Catch per Unit Effort (CPUE) data. The overall data was monthly average data in 2019 with fishing ground areas in the Western waters of Sumatra, the Indian Ocean. The results showed the composition of catches in the waters of West Sumatra landed in PPN Sibolga there are three dominant types of fish, namely skipjack tuna 14.566.140 kg (49.90%), decapterus 6.404.470 kg (21.94%) and tunny 2.480.880 kg (8.50%), The dynamics of fish catches in PPN Sibolga in 2019 were highest in May at 3.945.143 kg and June was the lowest catch month of 1.093.292 kg and the average monthly catch in 2019 was 2.508.436 kg, the catch per business unit landed in PPN Sibolga in 2019 obtained the highest CPUE of 8.474 kg/trip (July 2019) and the lowest 1,755 kg/trip (June 2019). ABSTRAK Overfishing dan overcapacity erupakan masalah keberlanjutan pembangunan perikanan tangkap. Indonesialah mengalami overfishing atau disebut penangkapan berlebih dan overcapacity atau disebut kelebihan kapasitas penangkapan. Pantai Barat Pulau Sumatera memiliki potensi perikanan yang sangat besar, baik perairan teritorial maupun perairan ZEE. Tujuan dari penelitian adalah untuk memahami trend fluktuasi hasil tangkapan ikan di Perairan Barat Sumatera, mengkaji pengaruh trip kapal dengan hasil tangkapan ikan di Perairan Barat Sumatera dan memberikan informasi dasar dan pengelolaan perikanan di Perairan Barat Sumatera. Materi penelitian yang digunakan adalah data Catch per Unit Effort (CPUE). Keseluruhan data merupakan data rata-rata bulanan tahun 2019 dengan daerah fishing ground Perairan Barat Sumatera Samudera Hindia. Hasil penelitian menunjukkan komposisi hasil tangkapan di Perairan Barat Sumatera yang didaratkan di PPN Sibolga terdapat tiga jenis ikan yang dominan yaitu cakalang 14.566.140 kg (49,90%), layang 404.470 kg (21,94%) dan tongkol 2.480.880 kg (8,50%), Dinamika hasil tangkapan ikan di PPN Sibolga di tahun 2019 tertinggi terjadi pada bulan Mei sebesar 3.945.143 kg dan bulan Juni merupakan bulan hasil tangkapan terendah yaitu 1.093.292 kg dan rata-rata hasil tangkapan bulanan tahun 2019 adalah 2.508.436 kg, Hasil tangkapan per-unit usaha yang didaratkan di PPN Sibolga di tahun 2019 didapatkan CPUE tertinggi yaitu 8.474 kg/trip (Juli 2019) dan terendah 1.755 kg/trip (Juni 2019). Kata Kunci: CPUE, penangkapan berlebih, penangkapan ikan, PPN Sibolga, Perairan Barat Sumatera

Evaluating and predicting impacts of Australian redclaw crayfish Cherax quadricarinatus and Louisiana red swamp crayfish Procambarus clarkii invasions

Freshwater crayfish have become one of the most widely introduced freshwater taxa globally. Crayfish introductions have not spared the African continent, which, apart from Madagascar, is naturally devoid of native freshwater crayfish. These introductions are of concern because invasive crayfish have generally been shown to cause strong impacts on recipient ecosystems outside Africa. This study therefore set out to compile up-to-date information regarding crayfish introductions in Africa, their pathways and distributions and to improve our understanding of the nature and magnitude of their environmental impacts. A systematic review revealed that nine crayfish species have been introduced into the continent with five of those, Astacus astacus, Cherax quadricarinatus, Faxonius limosus, Procambarus clarkii and Procambarus virginalis, having established naturalised populations in fourteen African countries (Chapter 2). The main driver of these crayfish introductions was to provide socio-economic benefits but there is limited evidence of success. The thesis further documents attempts made to address crayfish knowledge gaps in Africa, including standardisation of C. quadricarinatus sampling gear (Chapter 3), determination of the distribution of C. quadricarinatus in the recently invaded Upper Zambezi Basin (Chapter 4), and predicting ecological and socioeconomic impacts of two crayfish species that are spreading rapidly in Southern Africa, namely, C. quadricarinatus and P. clarkii (Chapters 5 – 8). To standardise C. quadricarinatus sampling methods in Africa, two methods used in Southern Africa were compared and the Promar® collapsible trap baited with dry pellets was recommended as the best approach for C. quadricarinatus abundance studies due to the high catch per unit effort (CPUE), probability of capture and the suitability of dry dog food as a standard bait. This standard approach was used for crayfish surveys in the Zambezi Basin to comprehensively determine the spread and establishment of C. quadricarinatus across the basin. The establishment of C. quadricarinatus in the Barotse Floodplain, Upper Zambezi Floodplains freshwater ecoregion was confirmed. Although the probability of capture and catch per unit effort (CPUE) of C. quadricarinatus in the Barotse floodplain were similar to that of older invasions in the basin (Lake Kariba and Kafue River), morphometric differences among C. quadricarinatus populations sampled from these invaded regions were detected. Although crayfish were not detected in other regions, for example, the Okavango Floodplains ecoregions, C. quadricarinatus have the potential to spread at a downstream and upstream rate of 49 and 12 km·year-1, impacting native biota therein. To evaluate the potential for ecological impacts, the consumer-resource dynamics of C. quadricarinatus and P. clarkii were described in comparison to a native trophic analogue, the freshwater crab of the Potamonautes genus, preying on various native taxa ubiquitous to African aquatic and terrestrial ecosystems. The use of functional response (FR) and consumption experiments in this study showed the potential impacts of the two crayfish species on native resources and on resources that support livelihoods in invaded ecosystems. This in most cases was a result of their high attack parameter, which also resulted in high functional responses ratios (FRRs) compared to native crabs. The crayfish FR, FRRs and consumption rates were mostly enhanced under the high temperature treatments. The FRs and consumption results were then combined with the field biomasses of crayfish and crabs to calculate the relative impact potential (RIP) to successfully predict the degree of impact caused by crayfish species relative to crabs. Crayfish species consistently displayed RIP scores > 1 relative to the native crab irrespective of region, which were higher for the summer than the winter season, suggesting greater impact of the invaders compared to the native species. This study further estimated the socioeconomic losses due to catch spoilage by C. quadricarinatus which are up to 1500 t per year in the invaded Kafue River Basin, which translates to an annual income loss of US$ 2 million. Information provided in this study is vital for conservation management and to compel policymakers to develop appropriate conservation management tools within regulatory frameworks, which could stop or minimise the spread of crayfish species and protect Africa from further losing aquatic biodiversity.

Population characteristics of the non-indigenous round goby, Neogobius melanostomus (Actinopterygii: Perciformes: Gobiidae), in the eastern Gulf of Finland

The round goby, Neogobius melanostomus (Pallas, 1814), is a fish of Ponto-Caspian origin that has been invading the Baltic Sea since the 1990s. Currently, it is abundant and commercially important in some areas of the sea. This species was first reported in the eastern Gulf of Finland (GoF) in 2012. Its occurrence increased thereafter, however it has remained largely unstudied in this region. The aim of this study was to investigate the population characteristics of the round goby in the eastern GoF to better understand its expansion trend and whether it will become abundant enough to be exploited by the local fishery. Fish were caught using multi-mesh gillnets (12–60 mm mesh) and a beach seine (0.5–10 mm mesh). Occurrence, density, catch per unit effort, biomass per unit effort, relative number and biomass in catches, as well as age, size and sex ratio were studied. The species regularly occurred in samplings along the southern coastline of the GoF, as well as some central areas and along the northern coast. Within 2012–2019, its occurrence in catches increased, with the highest frequency in 2015–2019 in shallow waters (<1.5 m) of Koporye Bay (70%) and in the deeper waters of Narva Bay (74%). Similarly, the highest density in the shallow waters was also observed in Koporye Bay (10.0 ind. ∙ 100 m−2), and offshore in Narva Bay. Relative abundance and biomass usually did not exceed 23%, although it reached 93% in Narva Bay. The oldest specimen was five years old. Young-of-the-year (YOY) juveniles predominated in the shallow waters (85%), while three-year-olds prevailed in deeper waters (75%). Among the fish older than two years, females were more predominant (mean ratio 3 to 1), and males were larger than females. Specimens in all life stages were found in the eastern GoF, and their abundance increased annually, suggesting that the round goby has successfully colonized this region of the Baltic Sea. However, compared to other areas of the Baltic Sea inhabited by longer-established populations, its population size is still relatively low.