Comparison of the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus) tuna associated with drifting FADs in the equatorial central Pacific Ocean

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5–65.0 cm in fork length (FL)], 43 yellowfin (31.6–93.5 cm FL) and 32 bigeye tuna (33.5–85.5 cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100 m, but occasionally dived to around 150 m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow the selective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.     

基于线粒体COⅠ和Cytb基因序列的北太平洋柔鱼种群遗传结构研究

为准确掌握柔鱼的种群遗传结构,拟通过线粒体DNA的COI和Cytb基因序列分析方法对柔鱼不同产卵季节群体的遗传多样性和遗传结构进行研究。经PCR扩增与测序分别获得600 bp COI与481 bp Cytb基因序列。基于COI基因序列分析得到的单倍型数、单倍型多样性指数、核苷酸多样性指数及平均核苷酸差异数分别为24、(0.729 ±0.033)、(0.005 70 ± 0.003 25)和3.421。基于Cytb基因序列分析得到的单倍型数、单倍型多样性指数、核苷酸多样性指数及平均核苷酸差异数分别为28、(0.852 ± 0.016)、(0.006 45 ± 0.003 73)和3.101。分析认为, 北太平洋柔鱼2个产卵季节群体均具有较高的单倍型多样性指数和较低的核苷酸多样性指数。单倍型邻接树、两两群体间的F_st值以及AMOVA分析结果均表明, 北太平洋柔鱼2个产卵季节群体间的遗传差异不显著, 不存在显著的群体遗传结构。初步认为, 该海域因缺乏地理上的障碍, 加之北太平洋海流的作用以及柔鱼个体较强的游泳能力, 使得群体之间具有较强的基因流。     

Population structure of bigeye tuna (Thunnus obesus) in the Indian Ocean inferred from mitochondrial DNA

Population structure of bigeye tuna (Thunnus obesus) in the Indian Ocean, Western Pacific Ocean and Eastern Atlantic Ocean were investigated using mitochondrial (mt) DNA sequence data. A total of 380 specimens were sampled from four regions in the Indian Ocean (Cocos Islands, Southeastern Indian Ocean, Southwestern Indian Ocean and Seychelles), and one region each from the Atlantic (Guinea) and the Western Pacific Oceans, respectively. The reconstructed neighbor-joining phylogeny based on the first hypervariable region (HVR-1) of the mitochondrial control region sequence data showed that haplotypes from the Indian and the Western Pacific Oceans could be grouped into two clades (Clades I and III), whereas in the Atlantic Ocean, two divergent clades (Clades I and II) coexisted. A single stock of bigeye tuna in the Indian Ocean was supported by hierarchical AMOVA tests and pairwise Φ_ST analyses. Clade I was the dominant population in the Indian and the Western Pacific Oceans which consisted of more than 96% of the specimens and Clade II was a specific group exclusively restricted to the Atlantic Ocean which made up 77% of its specimens. A new minor Clade, Clade III was discovered in the Indian and the Western Pacific Ocean. Overall, these analyses indicated that bigeye tuna of the Indian Ocean constituted a single panmictic population.     

Application of a habitat-based model to estimate effective longline fishing effort and relative abundance of Pacific bigeye tuna (Thunnus obesus)

A new habitat‐based model is developed to improve estimates of relative abundance of Pacific bigeye tuna (Thunnus obesus). The model provides estimates of `effective' longline effort and therefore better estimates of catch‐per‐unit‐of‐effort (CPUE) by incorporating information on the variation in longline fishing depth and depth of bigeye tuna preferred habitat. The essential elements in the model are: (1) estimation of the depth distribution of the longline gear, using information on gear configuration and ocean currents; (2) estimation of the depth distribution of bigeye tuna, based on habitat preference and oceanographic data; (3) estimation of effective longline effort, using fine‐scale Japanese longline fishery data; and (4) aggregation of catch and effective effort over appropriate spatial zones to produce revised time series of CPUE. Model results indicate that effective effort has increased in both the western and central Pacific Ocean (WCPO) and eastern Pacific Ocean (EPO). In the WCPO, effective effort increased by 43% from the late 1960s to the late 1980s due primarily to the increased effectiveness of effort (deeper longline sets) rather than to increased nominal effort. Over the same period, effective effort increased 250% in the EPO due primarily to increased nominal effort. Nominal and standardized CPUE indices in the EPO show similar trends – a decline during the 1960s, a period of stability in the 1970s, high values during 1985–1986 and a decline thereafter. In the WCPO, nominal CPUE is stable over the time‐series; however, standardized CPUE has declined by ～50%. If estimates of standardized CPUE accurately reflect relative abundance, then we have documented substantial reductions of bigeye tuna abundance for some regions in the Pacific Ocean. A decline in standardized CPUE in the subtropical gyres concurrent with stability in equatorial areas may represent a contraction in the range of the population resulting from a decline in population abundance. The sensitivity of the results to the habitat (temperature and oxygen) assumptions was tested using Monte Carlo simulations.     

Natal origin and population connectivity of bigeye and yellowfin tuna in the Pacific Ocean

Natural chemical markers (stable isotopes and trace elements) in otoliths of bigeye tuna (Thunnus obesus) and yellowfin tuna (T. albacares) were used to investigate their origin and spatial histories in the western and central Pacific Ocean (WCPO). Otolith chemistry of young‐of‐the‐year (YOY) T. obesus and T. albacares from four regions in the WCPO was first determined and used to establish baseline chemical signatures for each region. Spatial variation in stable isotope ratios of YOY T. obesus and T. albacares was detected, with the most noticeable difference being depleted otolith δ¹⁸O values for both species from the far west equatorial and west equatorial regions relative to the central equatorial and Hawaii regions. Elemental ratios in otoliths were also quantified for YOY T. obesus and T. albacares collected in 2008, and several showed promise for distinguishing YOY T. obesus (Mg:Ca, Mn:Ca, and Ba:Ca) and T. albacares (Li:Ca and Sr:Ca). The natal origin of age‐1 to age‐2+ T. obesus and T. albacares was then determined for two regions of the WCPO, and mixed‐stock analysis indicated that T. obesus and T. albacares in our west equatorial sample were almost entirely from local production, with a minor contribution from central equatorial waters. Similarly, T. albacares collected in Hawaii were exclusively from local sources; however, a large fraction of T. obesus in Hawaii were classified to the central equatorial region, suggesting that the movement of migrants from outside production zones (i.e., south of Hawaii) are important to Hawaii's domestic fishery.     

Vertical behavior of bigeye tuna (Thunnus obesus) in the northwestern Pacific Ocean based on archival tag data

The behavior of bigeye tuna (Thunnus obesus) in the northwestern Pacific Ocean was investigated using archival tag data for 28 fish [49–72 cm fork length (FL) at release, 3–503 days] released in Japanese waters around the Nansei Islands (24–29°N, 122–132°E) and east of central Honshu (Offshore central Honshu, 32–36°N, 142–148°E). Vertical behavior was classified into three types based on past studies: ‘characteristic’ (non‐associative), ‘associative’ (associated with floating objects) and ‘other’ (behavior not fitting into these two categories). The proportion of fish showing associative behavior decreased and that of characteristic behavior increased as fish grew, and this shift was pronounced at 60–70 cm FL. The fish usually stayed above the 20°C isotherm during the daytime and nighttime when showing associative behavior and below the 20°C isotherm during daytime for characteristic behavior. A higher proportion of characteristic behavior was seen between December and April around the Nansei Islands, and between September and December for offshore central Honshu. Seasonal changes in vertical position were also observed in conjunction with changes in water temperature. In this study, ‘other’ behavior was further classified into five types, of which ‘afternoon dive’ behavior, characterized by deep dives between around noon and evening, was the most frequent. The present study indicated that in the northwestern Pacific Ocean, the vertical behavior of bigeye tuna changes with size, as well as between seasons and regions.     

Do habitat models accurately predict the depth distribution of pelagic fishes?

Habitat models are used to correct estimates of fish abundance derived from pelagic longline fishing gear. They combine information on hook depth with the species’ preferences for ambient environmental conditions to adjust the gear's catchability. We compare depth distributions of bigeye tuna (Thunnus obesus) catch predicted by a habitat model with distributions derived from data collected by observers on longliners in the tropical Pacific Ocean. Our analyses show that the habitat model does not accurately predict the depth distribution of bigeye tuna; its predictions are worse than those from models that assume no effect of depth on catches. Statistical models provided superior fits to the observed depth distribution. The poor performance of the habitat model is probably due to (1) problems in estimating hook depth, (2) fine‐scale variations in environmental conditions, (3) incomplete knowledge of habitat preferences and (4) differences between the distribution of bigeye tuna and their vulnerability to longline gear.     

Genetic population structure of the Pacific bluefin tuna Thunnus orientalis and the yellowfin tuna Thunnus albacares in the North Pacific Ocean

The genetic population structure of the Pacific bluefin tuna (PBF) Thunnus orientalis and the yellowfin tuna (YFT) T. albacares in the North Pacific Ocean was investigated. The polymorphism of microsatellite (SSR) loci and sequences of mitochondrial DNA control region (mtCR) were analyzed for 71 samples of PBF from Japan and Mexico and 45 samples of YFT from Japan and Panama. In the SSR analyses, both single-locus (?0.010 to 0.008 in PBF and ?0.023 to 0.020 in YFT) and global multilocus (0.003 in PBF and ?0.002 in YFT) F _ST values among the geographic populations were low and not significant in these species. In the mtCR analyses, neither the neighbor-joining tree nor the minimum spanning network showed genetic differentiation among the geographic populations in each species. The pairwise F _ST values among the geographic populations of them (?0.005 in PBF and ?0.020 to ?0.014 in YFT) were low and not significant. Our SSR and mtCR data suggested that genetic differentiations were not evident among the eastern and western populations in the North Pacific Ocean either in PBF or in YFT. Mismatch distributions, demographic parameters, and neutrality tests suggested that sudden population expansion of PBF and YFT in the North Pacific Ocean occurred 628,000–731,000 and 450,000–525,000 years ago, respectively.     

El Niño effects in the Palmyra Atoll region: oceanographic changes and bigeye tuna (Thunnus obesus) catch rate variability

A generalized additive model (GAM) was constructed to separate and quantify the effects of fishery‐based (operational) and oceanographic parameters on the bigeye tuna (Thunnus obesus) catch rates at Palmyra Atoll in the central Tropical Pacific. Bigeye catch, the number of hooks per set, and set location from 4884 longline sets spanning January 1994 to December 2003 were used with a temporally corresponding El Niño‐Southern Oscillation (ENSO) indicator built from sea surface height (SSH) data. Observations of environmental data combined with the results from the GAM indicated that there is an increase in bigeye catch rates corresponding to an increase in eastward advection during the winter months of El Niño events. A seasonal pattern with higher bigeye catch rates from December to April and a spatial pattern with higher rates to the northeast and northwest of the atoll were observed during this study period. It is hypothesized that the combination of the eastward advection of the warm pool coupled with vertical changes in temperature during the winter months of El Niño events increases the availability of bigeye tuna in this region. This increase in availability may be due to a change in exploitable population size, location, or both.     

Catch trend of bigeye tuna <Emphasis Type="Italic">Thunnus obesus</Emphasis> by purse seine using fish aggregating devices,by flag states and area of operation in tropical regions of the Western and Central Pacific Ocean

Seventeen members and cooperating non-members (CCMs) of the Western and Central Pacific Fisheries Commission (WCPFC) were responsible for 86% of the total catch of bigeye tuna Thunnus obesus by purse seine fishing from 2012 to 2014. We categorize the CCMs into an eastern, western and “other” group based on their main fishing areas. We found significant differences in the bigeye tuna catch per fish aggregating device (FAD) between the eastern group and the western group. We also estimated that the eastern group achieved a higher catch of bigeye tuna because of their increased fishing effort using FAD in the eastern area where there is a higher catch per unit effort for FAD. The regression analysis found significant correlations between the annual catch of bigeye tuna and the number of FAD sets. The average catch of bigeye tuna per single FAD set, estimated from the slope of the regression line, was 7.1 t in the eastern area and 2.7 t in the western area. An impact and risk plot composed of the slope of the regression line and the catch of bigeye tuna by each individual CCM was developed to improve management measures. Appropriate measures for the sustainable use of tuna resources in the region are discussed.     

基于线粒体Cyt b基因的黄鳍马面鲀种群分析

采用线粒体细胞色素b(cytochrome b,Cyt b)基因片段为遗传标记,分析了南海北部陆架和南沙西南部陆架海域5个黄鳍马面鲀群体的遗传结构,以判定南海北部不同海域之间及南海北部与南沙西南部陆架海域黄鳍马面鲀的种群归属。结果表明,在156个个体的779 bp Cyt b同源序列中共检测到56个变异位点和58种单倍型,5个群体间遗传距离为0.002 95~0.004 15,遗传分化性呈现出高单倍型多样性(0.820 1~0.980 4)和低核苷酸多样性(0.002 62~0.004 69)的特点;分子方差分析和遗传分化指数显示,黄鳍马面鲀的遗传变异来自群体内个体间,群体间无显著遗传分化;单倍型网络结构图和群体系统发育树结构均未出现明显的以地方群体为单位的家系式分支或者聚簇。比较5个不同地理群体间的遗传发育关系并结合种属界定标准判定,南海北部和南沙西南部陆架5个黄鳍马面鲀群体属于同一个种群。     

运用生产力-易捕率指数对10种热带太平洋鲨鱼种群的研究

热带太平洋是全球产量最高的金枪鱼渔场,大洋性鲨鱼种群遭受金枪鱼渔业的影响受到国际社会的高度关注。由于缺少渔业统计资料,一般难以运用标准的资源评估方法对这些兼捕的种类进行评估。笔者运用种群生产力-易捕率分析（productivity-susceptibility analysis,PSA）方法,对热带太平洋10种鲨鱼遭受金枪鱼延绳钓渔业影响的风险程度进行比较分析,并计算风险指数（vulnerability）。风险指数从低到高的种类依次为锤头双髻鲨（Sphyrna zygaena）、路氏双髻鲨（S.lewini）、无沟双髻鲨（S.mokarran）、尖吻鲭鲨（Isurus oxyrinchus）、狐形长尾鲨（Alopias vulpinus）、长鳍真鲨（Carcharhinus longimanus）、大青鲨（Prionace glauca）、镰状真鲨（C.falciformis）、浅海长尾鲨（A.pelagicus）、大眼长尾鲨（A.superciliosus）,表明大眼长尾鲨种群受延绳钓渔业影响而遭受过度捕捞的潜在风险最高,垂头双髻鲨的风险最低。该研究结果可以为热带太平洋金枪鱼延绳钓渔业的管理和生态系统保护提供科学参考。     

The lack of genetic differentiation of pacu (Piaractus mesopotamicus) populations in the Upper-Paraguay Basin revealed by the mitochondrial DNA D-loop region: Implications for fishery management

Pacu (Piaractus mesopotamicus) is an important fish species for professional and sport fisheries in the Alto-Paraguay Basin, located in the central western Brazil. In this study the D-loop control region of mtDNA sequence data was used to investigate genetic variability within and among populations of pacu. A total of 99 individuals were collected in the Paraguay River and in four other main tributaries. From these, 27 different haplotypes were observed. The overall nucleotide diversity and haplotype diversity were high in all sampling sites with 0.013 ± 0.001 and 0.840 ± 0.035, respectively. Hierarchical AMOVA analysis showed that pacu populations form a single panmictic population with low Φ_ST = ?0.0012 (p = 0.486) and high gene flow among rivers. Despite high genetic variability, the total capture officially landed in the Upper-Paraguay River Basin has been decreasing steadily during the last years with indications of overexploitation. Taking into account the heterogeneity of habitats, continuous anthropogenic disturbances and lack of genetic structure, it appears that fish from these sampling sites function as a metapopulation, a framework that may be applied to long term fishery management of pacu in the Panatanal.     

Considerations on diving patterns of bigeye tuna Thunnus obesus based on archival tag data

Swimming depth and selected environmental factors were examined using 2764 days of archival tag data for 18 bigeye tuna Thunnus obesus (fork length at release 58.5 ± 7.2 cm) that were captured, tagged, and released into Japanese waters. Daytime swimming depth was deeper with increasing body length. The lowest temperature encountered was usually about 10 °C or slightly higher. A positive correlation between swimming depth and light intensity at the ocean surface was dominant for during both daytime and nighttime. Synchronicity of swimming depth with deep scattering layer (DSL) was observed, except around midday. Deep diving to depths exceeding 550 m was observed a mean of 0.30 dives/fish/day. Based on the classification and analyses of deep diving pattern and consideration of environmental data, deep diving was assumed to be undertaken for the purposes of foraging, predator avoidance, and exploration of bathymetry, as well as due to aberrant behavior. Occasionally, extremely deep diving events exceeding 1000 m (maximum 1616 m) were recorded. Bigeye tuna appear to have high visual acuity and tolerance of both low and wide temperature ranges, and low dissolved oxygen content. Thus, probably bigeye tuna swimming depth is primarily adjusted based on prey distribution.     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Bigeye tuna (Thunnus obesus) vertical movements in the Azores Islands determined with pop-up satellite archival tags

Movement patterns of 17 bigeye tuna (Thunnus obesus) near the Azores Islands were analyzed between April and May 2001 and 2002 using pop‐up satellite archival tags. Despite short attachment durations (1 to 21 days, 8.2 days on average), their vertical movements revealed much shallower distribution of bigeye tuna in comparison with previous studies in the tropical Pacific and tropical Atlantic. Depth and temperature histograms were unimodal, although overall depth distribution during the day was deeper than during the night due to daily incursions in deeper waters. Although generalized additive models showed significant non‐linear relationships with weight of the fish and sea level anomaly (as a proxy for variability of thermocline depth), the effect of these variables on bigeye depth appeared minor, suggesting that vertical movements of bigeye in the Azores during the spring migration may be influenced by food availability in upper water layers.     

A comparison of circle hook and J hook performance in a western equatorial Atlantic Ocean pelagic longline fishery

Catch composition, catch rates, hooking location, and status at release at haulback were monitored during 81 experimental sets (launches and hauling fishing per day) in a commercial pelagic longline fishery targeting tuna in the equatorial South Atlantic Ocean. Circle hooks (size 18/0, 0° offset) and J-style hooks (size 9/0, 10° offset) with squid baits were deployed in an alternating fashion. The catch composition was not significantly different for most species between the two types of hooks, except for bigeye tuna, which showed a significantly higher proportion of catches on the circle hook (p ? 0.001) and for sailfish, pelagic stingray, and leatherback sea turtle, which had higher catch rates on the J-style hook (p = 0.018, p ? 0.001, and p = 0.044, respectively). Bigeye and yellowfin tuna showed significantly higher rates of survival at the time of gear retrieval with circle hooks, and circle hooks hooked bigeye tuna, yellowfin tuna, swordfish, and sailfish significantly more often externally than internally. Our results suggest that the use of size 18/0, 0° offset circle hooks in the equatorial pelagic longline fishery may increase the survival of bycatch species at the time of gear retrieval with minimal effects on the catches of target species.     

中国金枪鱼围网船队大眼金枪鱼渔获物的特征变化与人工集鱼装置禁渔期的关系

研究了2012-2015年中国金枪鱼围网船队大眼金枪鱼(Thunnus obesus)渔获物的特征变化与人工集鱼装置(fish aggregation devices,FAD)禁渔期的关系,文章收集了2012-2015年中国大陆金枪鱼围网船队在中西太平洋的渔捞日志数据,对随附鱼群捕捞努力量与小体大眼金枪鱼和大体大眼金枪鱼的船均产量进行分析比较。结果显示:1)从2013年开始,对随附鱼群投网的次数占总投网次数的比例有所降低,均不超过50%;2)K-S检验显示研究期内禁渔期前后的船均随附鱼群网次存在显著差异(P0.05);3)2013-2015年大眼金枪鱼渔获量的平均水平明显低于2012年;4)从2013年开始,禁渔期结束后的第一个月(即11月)的船均产量都发生猛增;5)从捕捞努力量与渔获量的相关性结果看,不论是小体大眼金枪鱼还是全部大眼金枪鱼,2013年和2014年两者都呈现出显著的强正相关关系(P0.05)。这些结果表明2012年以后中国船队对大眼金枪鱼幼鱼的兼捕水平有所下降,延长FAD禁渔期的管理措施对于保护大眼金枪鱼幼鱼在某些年份可能具有一定的效果。     

大西洋南部金枪鱼渔场的生产调查报告

根据随船调查材料，对大西洋南部金枪鱼延绳钓渔业从捕捞技术，渔场环境因素，渔获物情况、初加工、销售等方面做出了总结。本文着重分析了各个作业渔场的渔获情况，判断出八个中心渔场的位置，并就大眼金枪鱼在这几个中心渔场的生物学特征做了统计分析，从而为用地理信息技术预报渔场提供了实施依据。     

Tuna and swordfish catch in the U.S. northwest Atlantic longline fishery in relation to mesoscale eddies

To analyze the effects of mesoscale eddies, sea surface temperature (SST), and gear configuration on the catch of Atlantic bluefin (Thunnus thynnus), yellowfin (Thunnus albacares), and bigeye tuna (Thunnus obesus) and swordfish (Xiphias gladius) in the U.S. northwest Atlantic longline fishery, we constructed multivariate statistical models relating these variables to the catch of the four species in 62 121 longline hauls made between 1993 and 2005. During the same 13‐year period, 103 anticyclonic eddies and 269 cyclonic eddies were detected by our algorithm in the region 30–55°N, 30–80°W. Our results show that tuna and swordfish catches were associated with different eddy structures. Bluefin tuna catch was highest in anticyclonic eddies whereas yellowfin and bigeye tuna catches were highest in cyclonic eddies. Swordfish catch was found preferentially in regions outside of eddies. Our study confirms that the common practice of targeting tuna with day sets and swordfish with night sets is effective. In addition, bluefin tuna and swordfish catches responded to most of the variables we tested in the opposite directions. Bluefin tuna catch was negatively correlated with longitude and the number of light sticks used whereas swordfish catch was positively correlated with these two variables. We argue that overfishing of bluefin tuna can be alleviated and that swordfish can be targeted more efficiently by avoiding fishing in anticyclonic eddies and in near‐shore waters and using more light sticks and fishing at night in our study area, although further studies are needed to propose a solid oceanography‐based management plan for catch selection.