393,646 Gulf Menhaden (Brevoortia patronus) in the Alabama River

Researchers studying fish assemblages in the Alabama River netted 393,646 gulf menhaden, a remarkable collection because this species had previously been unrecorded from this tributary.  Scientists investigating the fish composition of the Alabama River  used nets to sample 19 sand and gravel bars from mile 22.9 to mile 72.  They sampled night and day as well as seasonally.  In all they collected 48 species from 41 sampling locations.  They discovered 2 other species previously unrecorded from the Alabama River–gulf killifish (Fundulus grandis) and inland silverside (Menidia beryllina).  The purpose of this study was to compare their fish survey with past collections to gain insight into how fish assemblages change over time.  180 fish species have been recorded from the Alabama River including 33 found nowhere else in the world.  The scientists who conducted their study found low similarity between their sampling and past collections.

Gulf menhaden.  Formerly unknown in the Alabama River, it is now perhaps the most abundant species there.

Tombigbeerivermap.png

Map of the Coosa, Alabama, and Tombigbee Rivers.  Incidentally, an ornithologist from Auburn University claims to have seen an ivory-billed woodpecker in the bottomland forests of the Tombigbee River.

River conditions change drastically over time.  Dike-building, damming, and dredging greatly alter modern day river patterns, thus influencing the composition and abundance of various fish species.  But before man colonized southeastern North America, changes in climate also greatly altered river patterns.  During cold dry climate stages, rivers changed into braided patterns, shrinking in size and becoming clogged with sand bars.  Flooding was far less common.  Sudden shifts to warm climate phases transformed rivers to a supermeandering pattern when massive floods were common.  Eventually, rivers settled into a normal meandering pattern with a moderate frequency of flooding, such as occurs today.  Meandering patterns create oxbow lakes–an habitat favorable for bass, crappie, and sunfish.  The changing river patterns of the Pleistocene undoubtedly caused fish assemblages to change in abundance and variety of species.  It would be interesting if we could go back in time and sample rivers at intervals of a century for tens of thousands of years.  Probably, no 2 samples would show any similarity.  Changing conditions created favorable habitat for some species, but chance colonization probably played an important role in fish species abundance and composition.  The prevalence of gulf menhaden in the Alabama River is an example of a chance colonization when a species just happens to find new habitat.

Reference:

Haley, T. Heath; and Carol Johnston

“Fish Assemblage on Sand/Gravel Bar Habitat in the Alabama River, Alabama”

Southeastern Naturalist 13 (3) 2014

*****

I just began subscribing to the Southeastern Naturalist.  I realized I was interested in every article this journal publishes, and the material will provide endless speculative fodder for my blog.  I do have 1 complaint about this journal, however.  I’ve noticed a fetish for complex statistics in many of the articles that get published.  I believe charts of raw data would be much more interesting than complex statistics understood by few other than statisticians.  For example the above referenced article becomes weighted down with a statistical analysis when charts of just the raw data would have been more interesting.  I would like to have seen charts of every species of fish surveyed along with how many, when, and where each specimen was caught.  This chart could have been compared with a chart of species sampled from historical collections.  Everybody reading the article would have understood this data, but I doubt anybody, other than the authors, fully understood their statistical analysis.

 

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