Freshwater fishes

Selecting sites that are of potential ecological value in promoting the diversity of freshwater and anadromous fishes in the St. Lawrence basically involves finding sectors that maximize the indicators that we have developed (species richness, rarity and conservation status). Such sectors are composed of a mosaic of habitats that, taken together, support the high biodiversity observed. In enhancing and protecting the best examples of these habitats, factors operating on a much larger scale must be taken into account. Large rivers like the St. Lawrence are complex ecosystems that are influenced by numerous factors at a number of different spatial and temporal scales (Amoros and Petts 1993). Some of these factors, such as the amount of water available at different times of the year, depend on the continental climatic regime. Variations in flow rate, and concomitant changes in water level, affect to different degrees the mosaic of habitats making up a large river like the St. Lawrence. Other important factors such as water quality and human-induced changes must also be considered in maintaining areas of high biodiversity.

The protection of sites with a high diversity of freshwater fish species must be seen in this context. These sites along the St. Lawrence were identified by examining maps of species richness, rarity and conservation status. To correctly interpret the maps, however, an analysis of hot spots on a finer scale is required. The first thing that must be noted is that species richness is not distributed randomly. The spatial autocorrelation of richness values was found to be significant at distances of roughly 10 km and less (Leclerc and DesGranges, forthcoming), which can therefore be defined as the maximum size for hot spots. It is still significant at distances ranging from roughly 40 km to 60 km, which corresponds to the distance between hot spots. Rarity and conservation status indices were also found to be autocorrelated, but only at distances of less than 5 km. The significant spatial scale is therefore around 5–10 km. These results also support our use of 10 km ´ 10 km squares for terrestrial organisms, as we will discuss later.

We also compared the distribution of species richness, rarity and conservation status with that of known spawning grounds. The presence of spawning areas is strongly correlated with rarity and conservation status indices, but less so with species richness indices (Leclerc and DesGranges, forthcoming). The presence of spawning grounds, however, is not the only factor explaining the variation in these indices. For example, an examination of the three maps showed that areas of high diversity appear to be associated with the presence of islands. Lastly, it should be noted that, overall, the freshwater section of the river has greater species diversity than the freshwater or brackish water estuary. Therefore, priority sites should be proposed in each of these sections.

To summarize the information on the three biodiversity indices (species richness, rarity and conservation) on a single map (priority sites), we transformed the indices into rank values. The weighted rank correlation of the indices provided the following results:

The strongest correlation (0.82) is between rarity and conservation status, which indicates that rare species are often of the greatest concern. The weakest correlation (0.45) is between richness and conservation status, which shows that that efforts to protect rare species or species of concern should not be focused exclusively on sites with high species richness. A principal component analysis used to transform these correlations revealed that two axes were significant. Only the first axis (75% of variance) was retained, however, since it allowed sites to be identified where species richness, rarity and conservation status were all concentrated, in accordance with the approach used for terrestrial organisms. The second axis (20% of variance) detected sites of high species richness, but these sites had fewer rare species and species of concern. The weighting on the first axis of each index allowed an index of the potential of sites to be measured. As mentioned before, the weighting for freshwater fishes ((0.51 ´ richness) + (0.63 ´ rarity) + (0.59 ´ conservation status)) is similar to that (equal to 1) applied initially to terrestrial organisms.

The following maps show the distribution of priority sites. According to biodiversity indicators, the following sites number among those with the greatest potential. Readers should note that the map must be interpreted at a scale of 5-10 km and that the distribution of sites is related to the distribution of spawning grounds, the most important type of fish habitat to be protected.

Overall, the brackish-water estuary appears to be an area of moderate importance. A larger number of samples, however, would have no doubt allowed us to detect variations within the estuary, at a scale closer to 5-10 km. With the additional samples, we believe that the area around the Montmagny Islands and suites of habitats on the south shore (including the mouths of tributaries that are major spawning rivers) would emerge as important sites for the biodiversity of estuary fish species.

Saltwater fishes

Using the same method applied to freshwater fish, we generated a map of priority sites based on information from the biodiversity maps (species richness, rarity and conservation). The weighted rank correlation of the indices provided the following results:

As in the case of freshwater fishes, the strongest correlation (0.58) is between rarity and conservation and the weakest (0.33), between richness and rarity. The latter result is due no doubt to the fact that many of the rare species are vagrants from the Atlantic Ocean that show up from time to time in the St. Lawrence, a phenomenon that will probably increase with climate change (Tyler 1971).

A principal component analysis of the correlation matrix revealed two important axes. The first axis, which explained 66% of the variance, was retained because it is weighted in favour of the sites with high scores for species richness, rarity and conservation status. The second axis (22% of variance) is weighted in favour of sites with high species richness but with few rare species, and was not retained due to the need for a common approach for terrestrial and aquatic organisms. Each index on the first axis was weighted to calculate an index of the ecological potential of the sites: (0.54 ´ richness) + (0.55 ´ rarity) + (0.63 ´ conservation status). This index assigns a more or less equal weight to all three criteria, similar to the weighting used for freshwater fishes and terrestrial organisms.

The following map shows the distribution of priority sites. As readers will note, the southern Gulf, dominated by the Magdalen Plateau, contrasts with the northern Gulf, which is very diverse in terms of macrohabitats. The map synthesizes the information shown in greater detail on the individual base maps.

According to the map, the regions with the greatest potential in protecting biodiversity are:
-	boundary of the saltwater estuary and Gulf
-	Sept Îles Bay and surroundings
-	the area around Anticosti Island, which plays an important role in structuring the environment in the northern Gulf
-	Laurentien Channel
-	Esquiman Channel
-	southwest coast of Newfoundland
-	northwest coast of Newfoundland
-	mouth of Chaleur Bay
-	area east of Prince Edward Island

Other sectors, particularly in the Lower North Shore region, appear to have potential but there is still not enough data from these areas to draw any conclusions.

The priority sites shown on the map are larger (a preliminary analysis of the map indicates a scale of around 100 km) than the terrestrial and freshwater fluvial sites (which are around 10 km or less). This larger scale is associated not only with the resolution of the basic data once consolidated but also with the larger spatial scale of marine ecosystems compared with that of freshwater fluvial and adjacent terrestrial ecosystems in the St. Lawrence. In terms of scale, this map should be compared to other mapping themes such as biogeographical regions or productivity (Ardisson et al. 1990; Ghaminé et al. 1990; De Lafontaine et al. 1991; Brunel et al. 1998).

The map of priority sites does not allow coastal sites to be identified on a fine enough scale (less than 10 km) to correspond directly to adjacent terrestrial sites. This is mainly because of the resolution of the data as discussed earlier. The strong relationship between species diversity and habitat diversity favours the selection of structurally diverse coastal sites located within larger aquatic sectors of interest. Using habitat variables to replace the direct measurement of biodiversity can indeed often be useful in locating potential protected marine sites (Ward et al. 1999).

Restoration efforts are already being directed at coastal sites dominated by loose sediments, such as barrier beaches, lagoons and dune systems. One example is the Chaleur Bay barachois (Jacquaz et al. 1990). Similarly, tributaries emptying into the estuary and Gulf have been identified as priority sites due to their importance to the Atlantic Salmon. Other unique coastal marine sites also deserve attention, such as the wintering grounds of Barrow's Goldeneye, a species that will soon be accorded protected status (Robert et al. 1999). The location of these areas is well known but they still have yet to be properly characterized in terms of ice regime, depth, sediments, salinity, benthic productivity and diversity, and structural diversity. Ice-rafted boulders deposited in areas of fine sediment may also be significant, since they support invertebrates that are a key item in the diet of sea ducks. In pairing marine and terrestrial habitats, managers should pay close attention to coastal and pelagic sites bordering seabird colonies in order to ensure the future of these ecosystems, which are of great value given the significant input of nutrients from the guano of the thousands of birds that populate these colonies (Zelickman and Golovkin 1972).



Jacques Leclerc