Winter Spawning Season Research Articles

Coupling and de-coupling of the El Niño Southern Oscillation to the supply of larval fishes to benthic populations in the Hawaiian Islands.

Several recent high intensity ENSO events have caused strong negative impacts on the adult phases of foundational species in coral reef ecosystems, but comparatively little is known about how climatic variables related to recent ENSOs are impacting the supply of larvae to benthic populations. In marine fishes and invertebrates, reproductive adults and planktonic larvae are generally more sensitive to environmental variability than older, non-reproductive adults. Further, the transport of larvae in ocean currents may also be strongly ENSO dependent. The interactions between the dynamics of larval survivorship and larval transport could lead to population bottlenecks as stronger ENSO events become more common. We tested the predictions of this hypothesis around the Main Hawaiian Islands (MHI) by constructing a correlation matrix of physical and biological time series variables that spanned 11 years (2007-2017) and multiple ENSO events. Our correlation matrix included four types of variables: i. published ENSO indices, ii. satellite-derived sea surface temperature (SST) and chlorophyll variables, iii. abundance and diversity of larval fishes sampled during the late winter spawning season off Oahu, and iv. abundance and diversity of coral reef fish recruits sampled on the western shore of the Big Island of Hawaii. We found that the abundance and diversity of larval fishes was negatively correlated with the Multivariate El Niño Index (MEI), and that larval variables were positively correlated with measures of fall recruitment (September & November), but not correlated with spring-summer recruitment (May & July). In the MHI, SST variables were not correlated with the MEI, but two successive El Niño events of 2014-15 and 2015-2016 were characterized by SST maxima approaching 30°C. Two large pulses of benthic recruitment occurred in the 2009 and 2014 recruitment seasons, with > 8000 recruits observed by divers over the summer and fall months. Both events were characterized by either neutral or negative MEI indices measured during the preceding winter months. These patterns suggest that La Niña and the neutral phases of the ENSO cycle are generally favorable for adult reproduction and larval development in the spring and summer, while El Niño phases may limit recruitment in the late summer and fall. We hypothesize that episodic recruitment during non-El Niño phases is related to favorable survivorship and transport dynamics that are associated with the formation of pairs of anticyclonic and cyclonic eddies on the leeward sides (western shores) of the Main Hawaiian Islands.

Ecological effects of offshore wind farms on Atlantic cod (Gadus morhua) in the southern North Sea

Evaluating the ecological effects of the rapid expansion of offshore renewables at local, regional and ecosystem-wide scales is essential to understand the overall socio-ecological trade-offs also for other sectors such as fisheries. Hence, little is known about the ecological impact on demersal fish. To shed light on this topic, we studied the effects of an offshore wind farm in the southern North Sea on different life stages of Atlantic cod (Gadus morhua) using a combination of sampling methods at varying spatial and temporal scales. Our investigations of diet composition and trophic niches indicate that cod utilizes wind turbine piles with scour protection as feeding grounds. Furthermore, collected information on cod adults and early life stages during winter spawning season suggest that spawning activity occurred in winter across the wider wind farm area. We conclude that wind turbine foundations with a scour protection can function as artificial reefs that have local positive effects on the resilience of local cod populations. With our study we contribute to urgently needed observational evidence regarding the ecological impact of offshore wind farm installations to inform area-based management and future monitoring activities.

Growth variability of Pacific saury Cololabis saira larvae under contrasting environments across the Kuroshio axis: survival potential of minority versus majority

AbstractGrowth variability was examined for Pacific saury Cololabis saira larvae under contrasting environments across the Kuroshio axis, based on samples collected during the winter spawning season in 2013 and 2014. The growth rate index (residual of the otolith marginal 3‐day mean increment width from the linear regression on knob length) of larvae was compared among three areas: the inshore side of the Kuroshio axis, the Kuroshio axis, and the offshore side of the Kuroshio axis in relation to sea surface temperature (SST), salinity (SSS) and chlorophyll‐a (CHL) concentration. The larvae were more densely distributed in the Kuroshio axis and offshore areas of higher temperature and salinity and lower chlorophyll‐a concentration than in the inshore areas of lower temperature and salinity and higher chlorophyll‐a concentration. No marked differences in the growth rate index were found among the three areas, even though the larvae in the inshore areas showed slightly higher growth rates in 2013. Despite the broad ranges of environmental factors, no clear relationship between the growth rate index and any environmental factor was detected. The survival potential of Pacific saury larvae was considered to be at least comparable under contrasting environments across the Kuroshio axis. Such a geographical homogeneity is concluded to be attributable to compensable effects of physical and biological factors. We hypothesize that the minority under physically‐unfavorable but biologically‐favorable conditions on the inshore side of the Kuroshio axis could survive equally well as the majority under physically‐favorable but biologically‐unfavorable conditions around the Kuroshio axis and on the offshore side of the Kuroshio axis.

An approach to describe depth-specific periodic behavior in Pacific halibut (Hippoglossus stenolepis)

Correspondence between patterns of occupied depth and environmental cycles, called “depth-specific periodic behavior”, has been used to inform management of several flatfishes. However, little is known about depth-specific periodic behavior of Pacific halibut (Hippoglossus stenolepis), an important species in recreational, commercial and subsistence fisheries in the eastern North Pacific Ocean. To evaluate depth-specific periodic behavior of Pacific halibut, an approach was developed in which depth data from electronic tags were used to produce four types of complementary plots, including two-dimensional time series of depth, activity level derived from differencing adjacent depth recordings, periodograms, and wavelet transform coefficients. From a visual examination of the plots, daily depth-specific periodic behavior types, including diel, tidal, spawning, semi-lunar and lunar, were assigned to 37 individual Pacific halibut. Overall, the approach used in this study was useful for describing relatively short term depth-specific periodic behavior, but was less informative for understanding relatively long term behavioral patterns. The results suggest that patterns in occupied depth may be related to seasonal activities of Pacific halibut. Specifically, during the summer feeding season, fish most commonly behaved periodically on a diel scale or inactively laid on the seafloor, which was manifested as tidal periodicity as the height of the water column fluctuated above the fish. Both active swimming and inactivity on the seafloor may be related to different foraging strategies. During fall and spring migratory periods and the winter spawning season, no periodicity in depth-specific behavior was most common, which may correspond to directed movement over irregular bathymetry between feeding and spawning locations or to reproductive behaviors. Evidence of an additional reproductive behavior, spawning rises off the seafloor, was also observed during the winter spawning season. This approach for understanding the periodicity of occupied depth of Pacific halibut provides additional insight into the behavior of this iconic species. This knowledge perhaps may be used in the future to inform this species' management, such as refining estimates of susceptibility to capture and examining timing of movement among regulatory areas.

Occurrence and density of Pacific saury Cololabis saira larvae and juveniles in relation to environmental factors during the winter spawning season in the Kuroshio Current system

AbstractThe occurrence and density of Pacific saury Cololabis saira larvae and juveniles were examined in relation to environmental factors during the winter spawning season in the Kuroshio Current system, based on samples from extensive surveys off the Pacific coast of Japan in 2003–2012. Dense distributions of larvae and juveniles were observed in areas around and on the offshore side of the Kuroshio axis except during a large Kuroshio meander year (2005). The relationships of larval and juvenile occurrence and density given the occurrence to sea surface temperature (SST), salinity (SSS), and chlorophyll‐a concentration (CHL) were examined by generalized additive models for 10‐mm size classes up to 40 mm. In general, the optimal SST for larval and juvenile occurrence and density given the occurrence was consistently observed at 19–20°C. The patterns were more complex for SSS, but a peak in occurrence was observed at 34.75–34.80. In contrast, there were negative relationships of occurrence and density given the occurrence to CHL. These patterns tended to be consistent among different size classes, although the patterns differed for the smallest size class depending on environmental factors. Synthetically, the window for spawning and larval and juvenile occurrence and density seems to be largely determined by physical factors, in particular temperature. The environmental conditions which larvae and juveniles encounter would be maintained while they are transported. The survival success under the physically favorable but food‐poor conditions of the Kuroshio Current system could be key to their recruitment success.

Changes in Sperm Production, Sperm Motility, and Composition of Seminal Fluid in Caspian Brown Trout, Salmo trutta caspius, Over the Course of a Spawning Season

This study was carried out to evaluate milt quality in male Caspian brown trout (Salmo trutta caspius) over the course of the winter spawning season. Milt samples were collected biweekly during December and January. Chemical composition of seminal fluid, sperm production (milt volume, sperm density, spermatocrit,) and sperm motility characteristics (percentage and duration of motility) were measured. Milt volume, sperm density, osmolality, seminal minerals (Ca2+, Mg2+, K+, Na+, Cl−), and total protein gradually decreased over the spawning season. Glucose and triglyceride content of milt did not show significant changes over the spawning season. Milt pH and the percentage and duration of motility were comparatively stable, declining only at the end of the season. Significant positive correlations were found between sperm density and seminal minerals, total protein and spermatocrit; percentage of motile spermatozoa and seminal minerals, total protein; and duration of motility and K+, Cl−, total protein, and pH. Results show that season has a significant influence on milt quality in male Caspian brown trout, with the best milt being available at the beginning of spawning season.

Schooling pattern of eastern Bering Sea walleye pollock and its effect on fishing behaviour

Abstract Shen, H., Dorn, M. W., Wespestad, V., and Quinn, T. J. 2009. Schooling pattern of eastern Bering Sea walleye pollock and its effect on fishing behaviour. – ICES Journal of Marine Science, 66: 1284–1288 Walleye pollock (Theragra chalcogramma) form persistent midwater and near-bottom schools in the daytime during the winter spawning season in the eastern Bering Sea (EBS). Two spawning areas in the EBS, north of Unimak Island and near the Pribilof Islands, are the main fishing grounds. To study the schooling pattern of pollock and its effect on fishing behaviour on these two fishing grounds, a principal component analysis with instrumental variables was carried out using acoustic and observer data from 2003 and 2005. Significant differences between the school descriptors distinguished the schooling patterns among areas and years. The harvester, that is to say, the fishing vessel and its crew taken together, searched for fish aggregations, which were caught in a different manner when the schooling pattern changed. School density had a greater effect than school size on fishing behaviour. Aggregations were less dense in 2003 than in 2005, and the harvester tended to fish with longer tows, at higher speeds, when it encountered less dense aggregations.

The Bahamas’ Nassau grouper ( Epinephelus striatus) fishery – two assessment methods applied to a data – deficient coastal population

The Nassau grouper is an important fish species in the reef ecosystem of the Bahamas. It is subjected to intense exploitation by small-scale fisheries and is harvested with different fishing gears, primarily during the winter spawning season. The piecemeal nature of the fishing operations precludes an economically feasible way to compile data to assess the status of exploitation of the resource. There is public and governmental concern regarding over-exploitation of the Nassau grouper due to the numerous extinctions of spawning aggregations in the greater Caribbean. Due to the large size of the Bahamas archipelago, where many Nassau grouper spawning aggregations still occur, the collection of appropriate data for stock assessments is very difficult. In addition, stock assessment algorithms that are applicable to tropical, seasonally aggregating species are noticeably lacking. In this paper we present applications of analytical and hydroacoustic assessment algorithms to the Nassau grouper fishery in the Bahamas that could be implemented under data-limited conditions. The results of the analyses indicate that the methods generate consistent abundance and mortality rate estimates that are commensurable with a stock subjected to full exploitation.

Seasonal migration and environmental conditions of Pacific halibut Hippoglossus stenolepis, elucidated from pop-up archival transmitting (PAT) tags

Pop-up archival transmitting (PAT) tags were used to study the fall migration of halibut in the Gulf of Alaska (GOA). We tagged 6 Pacific halibut Hippoglossus stenolepis on summer feeding grounds in the eastern GOA and another 6 in the western GOA from June 13 to August 6, 2002. The tags were programed to be released from the fish on January 15, 2003, at the height of the winter spawning season: 10 tags successfully detached, transmitted archived environmental data (depth and temperature), and generated accurate latitude-longitude coordinates shortly after pop-up; 2 tags deployed off SE Alaska were lost. The tags revealed that 6 fish had moved a considerable distance (>200 km) between tagging and pop-up, and all of these had moved northward to some extent. The longest of the observed migrations was from the southern Alaska Peninsula to Yakutat Bay, a linear displacement of 1153 km; 4 fish showed little evidence of geographic displacement, exhibiting migra- tions that ranged only from 30 to 69 km. Although 2 fish had moved inshore by the end of the tagging period, all other fish had moved offshore regardless of their overall migration distance. The precise timing of offshore movements varied, beginning as early as August and as late as January. These observations generally corroborate conventional tagging, indicating migration of halibut toward winter spawning grounds in the northern GOA, and movement of fish to deep water in fall. However, no single stereotypic migration behavior was apparent, and a variety of vertical movement patterns and temperature profiles were observed. Halibut spent most time in waters of 5 to 7°C, but experi- enced temperatures ranging from 2.6 to 11.6°C. Depth observations ranged from 0 to 736 m, with summertime activity concentrated in depths from 0 to 400 m, and halibut that exhibited offshore movement were typically observed at 300 to 700 m by mid-winter. Vertical movement (short-period changes in depth) varied among fish and over time, with some fish displaying little vertical activity, others displaying short periods of activity, and still others displaying considerable activity throughout their time at liberty.

Identifying spawning behavior in Pacific halibut, Hippoglossus stenolepis, using electronic tags

Identifying spawning behavior in Pacific halibut, Hippoglossus stenolepis, is particularly challenging because they occupy a deep, remote environment during the spawning season. To identify spawning events, a method is needed in which direct observation by humans is not employed. Spawning behavior of seven other flatfish species has been directly observed in their natural environment by investigators using SCUBA. All of these flatfish species display almost identical spawning behavior that follows a routine. Therefore, it is reasonable to believe that this spawning behavior occurs in other flatfish species, including Pacific halibut. As part of a larger study, we recaptured two Pacific halibut on which Pop-up Archival Transmitting (PAT) tags had been attached during the winter spawning season. Because the tags were physically retrieved, we were able to collect minute-by-minute depth records for 135 and 155 days. We used these depth data to tentatively identify spawning events. On seven separate occasions between 20 January 2001 and 9 February 2001, one fish displayed a conspicuous routine only seen during the spawning season of Pacific halibut and the routine parallels the actions of other spawning flatfish directly observed by humans using SCUBA. Therefore, we propose this routine represents spawning behavior in Pacific halibut. The second tagged fish did not display the conspicuous routine, thus challenging the assumption that Pacific halibut are annual spawners. PAT tags may prove to be a useful tool for identifying spawning events of Pacific halibut, and that knowledge may be used for improved management in the future.

Tracing populations of Atlantic herring (Clupea harengus L.) in the Irish and Celtic Seas using otolith microstructure

Otolith microstructure of juvenile herring was used to distinguish autumn- and winter-spawned fish collected in the Celtic and Irish Seas in 1999 and 2000. Juveniles showed two distinct patterns of larval otolith growth; widely spaced increments (fast growers) and tightly packed increments (slow growers). Fast- and slow-growing fish exhibited a clear bimodal distribution and the two groups were completely distinct at increments 60–70. Otolith increment counts confirmed that the fast-growing fish originated from the winter spawning season and that slow-growing fish were spawned in autumn. This characteristic pattern of otolith growth was used to determine the relative proportions of autumn- and winter-spawned fish at nursery grounds in the Irish and Celtic Seas. Although the proportions in each area varied between years, nursery grounds in the western Irish Sea were generally dominated by winter-spawned fish whereas autumn-spawned fish were mostly at eastern stations. Given the distribution of spawning adults in the region, the vast majority of winter-spawned fish are likely to originate from the Celtic Sea. Larval growth differences between nursery areas suggest that Celtic Sea herring drift into the Irish Sea during the larval phase. There was significant variation in fish size between nursery areas for both autumn- and winter-spawned fish. Juvenile length was greatest in the Celtic Sea, intermediate in the eastern Irish Sea, and lowest in the western Irish Sea. Therefore, larval dispersal of Celtic Sea herring into the Irish Sea produces components in the surviving juvenile population with characteristic growth patterns. This population segregation could potentially impact on subsequent growth, survival and recruitment. 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.

Early Life Survival of the AnchovetaEngraulis ringensOff Central Chile during the 1995 and 1996 Winter Spawning Seasons

For fish populations occurring in coastal upwelling areas, the timing of spawning has been proposed to occur during seasons when transport offshore is reduced. Along the coastal zone off central Chile, the anchoveta Engraulis ringens spawns preferentially during winter. Spawning in this season, however, might represent a period of increased risk to eggs and larvae due to the harsh and variable oceanographic conditions. This study determined the mortality rates of egg and larval anchoveta in an area located close to the species' southern limit of distribution during its winter spawning season. Two temporal scales of variability, interseasonal (between years), and intraseasonal (individual daily cohort mortality rates) show that (1) mean seasonal mortality rates were not different between years and (2) mortality rates considering the egg and larval stages together (96% daily in 1995 and 98% daily in 1996) were much higher than those estimated using only the larval stage (4.4% daily in 1995 and 6.8% daily in 1996). The results of the individual cohort mortality rates, especially in 1995, revealed a tendency toward a decrease in mortality rates as the winter season progressed (from 52 to 9% daily). Because the maximum egg abundance in the water column occurred early in the season in 1995, we propose that the largest fraction of the mean seasonal mortality was due to egg mortality occurring early in winter. The information on the environmental characteristics and the reported larval growth rates in different periods during the winter spawning season do not support the hypothesis of larval food limitation but, instead, suggest that oceanographic factors (e.g., cross-shelf transport, low water temperature, presence of river plumes) play a major role in the development and success of the early life stages in this southern spawning area.

Epizoology of Hepatic Neoplasia in Atlantic Tomcod (Microgadus tomcod) from the Hudson River Estuary

Atlantic tomcod (Microgadus tomcod) collected from the Hudson River estuary during the winter spawning season revealed neoplastic and preneoplastic lesions in livers from 44% of the age 1 individuals and 93% of the age 2 individuals collected. These lesions appear as a continuum ranging from basophilic foci with little cellular alterations to hepatocellular carcinoma frequently involving the entire liver. Lesions were more prevalent in larger individuals within the same age group, suggesting a relationship between growth rate and tumor expression. Atlantic tomcod from a relatively unpolluted estuary in Connecticut did not reveal a comparable prevalence of hepatic lesions. Juvenile tomcod collected from the Hudson during the summer, only 4–5 mo prior to the winter spawning season had no hepatic lesions, suggesting that these lesions form rapidly, coincident with gonadal maturation. Chemical analysis of liver tissue revealed high levels of PCBs (2.5–38.2 mg/kg) and the presence of several pesticides including DDT (and metabolites), chlordane, and dieldrin (<0.1–3.0 mg/kg) and several heavy metals (<0.1–6.5 mg/kg). These results suggest that chemical contamination of the lower estuary nursery areas, coupled with high-temperature stresses of summer, may contribute to the high levels of hepatic lesions observed.

Ecological studies on two intertidal New Zealand fishes,Acanthoclinus fuscusandForsterygion nigripenne robustum

Abstract Population density, seasonal abundance fluctuations, and habitat preferences of Acanthoclinus fuscus and Forsterygion nigripenne robustum were studied in the rocky intertidal zone at Kaikoura, New Zjaland, from August 1988 to June 1989. Monthly recaptures of marked fishes showed that A. fuscus was common on rocky platforms with small shallow pools; F. n. robustum occurred under larger stones and in deeper channels or larger pools. Most captured A. fuscus were juveniles and adolescents; no seasonal fluctuation in abundance was recorded. The intertidal A. fuscus populations at Kaikoura and Auckland were similar in growth rate and condition factor but differed in age structure. The intertidal population of F. n. robustum was dominated by mature fish; the highest abundance was recorded during the winter spawning season. Each monthly sample of A. fuscus included 40% recaptures, significantly more than in F. n. robustum samples. 31% of displaced A. fuscus returned to their original pool within 1 day an...

Long-Term Adult Population Fluctuations and Distribution of the Spot, Leiostomus xanthurus, in Mississippi

Adult specimens of the spot, Leiostomus xanthurus, were collected from bayou, Mississippi Sound, and barrier island locations along the Gulf Coast of Mississippi from November 1982 to July 1989. The mean total length of all spot sampled in comparable gill net sets was 219 mm (± 14 standard deviation, n=4,338). Ninety-five percent of the spot were collected in the island and sound areas, where the salinity was higher than in the bayous. Catch per unit effort was high at island and sound stations in spring and autumn, with relatively few fish caught during the winter spawning season and summer. The relatively high frequency of spot observed at the island stations in the autumn was probably influenced by spawning migrations, and the high spring values may repesent a combination of two abundant year classes. The two greatest yearly collections, in 1983 and 1986, may have been influenced by sampling conditions or by environmental conditions favorable to survival either during those years or earlier when those fish were postlarvae. The smallest yearly catch occurred in 1985 and may have reflected the harsh weather conditions that year.