Skipjack

Abstract: In this paper we present a cryptanalytic technique, based on impossible differentials. We use it to show that recovering keys of Skipjack reduced from 32 to 31 rounds can be performed faster than exhaustive search. We also describe the Yoyo game (a tool that can be used against reduced-round Skipjack), and other properties of Skipjack.

Abstract: ABSTRACf Histological criteria to age postovulatory follicles were developed from examination of laboratory-spawned skipjack tuna; the criteria were used to estimate the frequency of spawning of skipjack tuna from the South Pacific. Examination of 87 skipjack tuna from field cOllections taken in October-November indicated that spawning occurred nearly every day. The fraction of mature females with postovulatory follicles, <24 hours old, was 0.85 (standard deviation = 0.071) indicating that the mean interval between spawn­ ings was only 1.18 days. Estimates of the frequency of spawning of multi­ ple spawning fishes are essential for understanding their reproductive biology. To estimate annual reproductive effort or fecundity, and how these variables are related to size or age structure of a population requires knowledge of the frequency of spawning and the number of eggs produced per spawning. Batch fecundity, the number of eggs pro­ duced per spawning, has been estimated for skipjack tuna a nwnber of times (see review by Matsumoto et al. 1984) but the spawning rate of the skipjack is unknown. Thus spawning frequency is one of the missing links in an assessment of the reproduction of skipjack populations. It has long been recognized that skipjack tuna spawn more than once in a season because more than one mode of advanced oocytes are found in active ovaries (Brock 1954; Bunag 1956; Joseph 1963; Raju 1964; Simmons 1969; Batts 1972; Cayre 1981; Goldberg and Au 1986). The frequency of occurrence of female black skipjack tuna, Eutkyn­ nus lineatus, throughout the spawning season with ovaries containing hydrated oocytes led Schaefer (1986) to conclude that the average interval be­ tween spawnings of black skipjack in the eastern tropical Pacific was 2.1-5.7 d depending on the region. Over the last 6 years, two methods have been developed for measuring the spawning rate of multi­ ple spawning marine fishes: One method is based on the frequency of ovaries containing hydrated

Abstract: IPCC-type climate models have produced simulations of the oceanic environment that can be used to drive models of upper trophic levels to explore the impact of climate change on marine resources. We use the Spatial Ecosystem And Population Dynamics Model (SEAPODYM) to investigate the potential impact of Climate change under IPCC A2 scenario on Pacific skipjack tuna (Katsuwonus pelamis). IPCC-type models are still coarse in resolution and can produce significant anomalies, e.g., in water temperature. These limitations have direct and strong effects when modeling the dynamics of marine species. Therefore, parameter estimation experiments based on assimilation of historical fishing data are necessary to calibrate the model to these conditions before exploring the future scenarios. A new simulation based on corrected temperature fields of the A2 simulation from one climate model (IPSL-CM4) is presented. The corrected fields led to a new parameterization close to the one achieved with more realistic environment from an ocean reanalysis and satellite-derived primary production. Projected changes in skipjack population under simple fishing effort scenarios are presented. The skipjack catch and biomass is predicted to slightly increase in the Western Central Pacific Ocean until 2050 then the biomass stabilizes and starts to decrease after 2060 while the catch reaches a plateau. Both feeding and spawning habitat become progressively more favourable in the eastern Pacific Ocean and also extend to higher latitudes, while the western equatorial warm pool is predicted to become less favorable for skipjack spawning.

Abstract: Skipjack tuna habitat in the western North Pacific was studied from satellite remotely sensed environment and catch data, using generalized additive models and geographic information systems. Weekly resolved remotely sensed sea surface temperature, surface chlorophyll, sea surface height anomalies and eddy kinetic energy data were used for the year 2004. Fifteen generalized additive models were constructed with skipjack catch per unit effort as a response variable, and sea surface temperature, sea surface height anomalies and eddy kinetic energy as model covariates to assess the effect of environment on catch per unit effort (skipjack tuna abundance). Model selection was based on significance of model terms, reduction in Akaike’s Information Criterion, and increase in cumulative deviance explained. The model selected was used to predict skipjack tuna catch per unit effort using monthly resolved environmental data for assessing model performance and to visualize the basin scale distribution of skipjack tuna habitat. Predicted values were validated using a linear model. Based on the fourparameter model, skipjack tuna habitat selection was significantly (P < 0.01) influenced by sea surface temperatures ranging from 20.5 to 26� C, relatively oligotrophic waters (surface chlorophyll 0.08‐0.18, 0.22‐0.27 and 0.3‐0.37 mg m )3 ), zero to positive anomalies (surface height anomalies 0‐50 cm), and low to moderate eddy kinetic energy (0‐200 and 700‐ 2500 cm 2 s ‐2 ). Predicted catch per unit effort showed a trend consistent with the north‐south migration of skipjack tuna. Validation of predicted catch per unit effort with that observed, pooled monthly, was significant (P < 0.01, r 2 = 0.64). Sea surface temperature explained the highest deviance in generalized additive models and was therefore considered the best habitat predictor.